Book OF Health

Malcolm, Mop^ris

ii

THE LIBRARY

OF

THE UNIVERSITY

OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND

MRS. PRUDENCE W. KOFOID

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THE BOOK OF HEALTH

THE

Book of Health.

BY

SIR RISDON BENNETT, M.D., F.R.S. JOHN S. BRISTOWE, M.D., F.R.S. J. CRICHTON BROWNE, LL.D., M.D.,

P.R.S. T. LA.UDER BRUNTON, M.D., F.R.S. JAMES CANTLIE, F.R.C.S. W. B. CHEADLE, M.D. CLEMENT DUKES, M.D. JOSEPH EWART, M.D. SIR JOSEPH FAYRER, K.C.S.I., F.R.S.

G. P. FIELD, M.R.C.S. MALCOLM MORRIS, F.R.C.S., Ed. SHIRLEY MURPHY, M.R.C.S. J. E. POLLOCK, M.D. HENRY POWER, F.R.C.S. J. RUSSELL REYNOLDS, M.D., F.R.S. W. S. SAVORY, F.R.S. CHARLES S. TOMES, F.R.S. FREDERICK TREVES, F.R.C.S. HERMANN WEBER, M.D.

EDITED BY

MALCOLM MOEEIS

C^irtr <!51iition.

CASSELL & COMPANY, Limited

LONDON, PARIS & NEW YORK.

1884. [all rights resekyed.]

PREFACE. Libvrcvy

The object of this Work is to place before the general reader, in an intelligible form, and in language free from technical obscurity, the principal rules that should be adopted for the preservation of Health. Directions for the treatment of disease are purposely omitted, for it is intended to teach, not how disease can be cured, but how it can be prevented. The laws of public and private hygiene are now matters of vital interest to all classes of society, and it is generally recognised that carelessness and ignorance often lead to the establish- ment or the spread of disease which might in the first instance have been easily avoided. No work of authority, however, existed to which those desirous of readily obtaining information on special subjects could refer; hence the present publication, in the production of which the Editor has been honoured with the co-operation of eminent members of the Medical Profession. To these gentlemen he begs to offer his sincere thanks.

THE EDITOR

iviSSCriS

CONTENTS

INTEODUCTOEY.

By W. S. Savory, F.R.S.

Surgeon to St. Bartholomew's Hospital.

PAGE

Life and Health— The Organic Functions— Digestion— Absorption— Circiilation of the Blood- Action of the Heart— Pulmonary Circulation— Eespiration— The Animal Functions- The Skeleton— Muscular and Nervous Systems— The Brain— Vital Sympathy— The Distinctive Features of Life— Waste and Eepair— Sleep— Dreaming and Somnambulism— Day- Dreams— Rhythmical Action— The Material Agents of Vital Action— Food and Air- The Relation of Physical Forces to Vital Action— Death— The Signs of Death— Health— Conditions Affecting Health— Man's Place in Nature 1

FOOD AND ITS USES IN HEALTH.

By Sir Risdon Bennett, M.D., F.R.S.,

Late President of the Boyal College of Physicians, London.

iTature and Requirements of Food — ^Alimentary Principles — Sources and Varieties of Food — Alimentary Substances — Animal Food — Vegetable Food — Fruits — Farinaceous Foods— Saccharine Substances —Water — Tea — Coffee — Cocoa — Condiments — Preparation of Food — Preservation and Employment of Food— Proportions of Different Kinds of Food — Supply of Liquids— Diets of Various Peoples— Deficiencies in Food— Times and Frequency of Meals- Diets of Different Ages of Life 101

THE INFLUENCE OF STIMULANTS AND NAECOTICS

ON HEALTH.

By T. Lauder Brunton, M.D., D.Sc, F.R.S.,

Assistant Physician to St BaHholomew's Hospital.

Introductory— The Value of Alcohol as a Food— The Effects of Alcohol— The .Causes of Intem- perance— Forms of Alcohol — Diseases Resulting from Excessive Use of Alcohol — Hereditary Effects of Alcohol — Alcohol in its Relations to Crime, Lunacy, and Pauperism — Ether — Opium — Chloral — Indian Hemp — Tobacco— Betel-nut— Tea— Coffee— Chocolate — Cocoa— Guarana— Cola-nut— Coca— Kava— Beef -Tea 18S

«iii

CONTENTS.

EDUCATION AND THE NERVOUS SYSTEM.

By J. Criohton Browne, M.D., LL.D., F.R.S., iord Chanctllor'a Visiior.

limiontTCTORY— Body-Growth Duties of Schoolmasters— School Registers and Life Charts- Tables of Height and "Weight— Brain-Growth— Quantity, Quality, and Structure of Brain- Balance of Parts of Brain and Functional Habits— Blood Supply— Periodicity and Educa- tion—Diurnal Changes— Sleep— Duration of Sleep— Depth of Sleep— Dreams— The Pro- motion of Sleei>— Morbid Modifications and Disturbances of Sleep— Nightmare— Night Terrors— Somnambulism— Morning and Evening Study— LuNAR Changes— Seasonal Chanoks— Vernal Excitement— Epochal Changes— Teething— Puberty— Physical Educa- tion—Exercise— Evolution of Cerebral Centres— Either-handed Education— Gymnastics- Degeneration from Over-use — Food — Alimentativeness — Morbid Appetites— Starvation — Varied Diet— Intellectual Education— Precocity— Natural Education— Kinder - Garten System— Brain-Forcing— Effects of Brain-Forcing— Cranial Injuries— School Headaches- Examinations— Moral Education— Parental Responsibilities— Family Life— Monasticism— School Discipline— The Natiiral System— Artificial Penalties— Corporal Punishment— Express Moral Lessons— Healthy Literature— Self-Examination— Volitional Exercises— Religious Education

THE INFLUENCE OF EXERCISE ON HEALTH.

By James Cantlie, M.B., F.R.C.S.,

Assistant Surgeon and Demonstrator of Anatomy, Charing Cross Eos'pital.

Introductory — Muscles— Blood Supply of Muscles— Respiration— Muscular Belongings — Effects of Exercise on Muscles — InsuflScient Exercise — Over-exertion — Girl's Work and Exercise — Training : its Dangers and its Use — ^Walking — Running— Jumping — Dancing — Riding — Skating— Rowing— Cricket— Football— First Aid to the Injured— Swimming— Lawn Tennis— Racquets— Bicycling and Tricycling— Other Games— Gymnastics— Calisthenics 381

THE INFLUENCE OF DEESS ON HEALTH.

By Frederick Treves, F.R.C.S. Eng., Assistant Swgeon to and Lecturer on Anatomy at the London Hospital.

Introductory- The Primary Objects of Clothing— The Materials used in Dress— The Comparative Value of Dress Materials as Articles of Clothing :—l. Warmth; 2. Hygroscopic Properties ; 3. Porosity; 4. Impermeability to. Water ; 5. Inflammability; 6. Power of Absorbing Odours ; 7. Electrical Qualities ; 8. Certain Poisonous Dyes— Underclothing— Fit Clothing for Exercise— Objections to Woollen Underclothing— Night Attire— Male Dress— The Head- Hats, Caps, etc.— The Neck— The Trunk and Extremities— Female Dress— The Head and Neck— Bonnets, Veils, etc.— The Trunk and Extremities— Underclothing— Tight Sleeves- Tight Lacing— A Hygienic Costume— The "Divided Skirt"— The Hands— The Feet- Stockings— Boots and Shoes— High-heeled Shoes -2%c Dress of Infancy and Childhood ... 461

CONTENTS. ^

THE INFLUENCE OF OUR SUREOUNDINGS ON HEALTH.

By James E. Pollock, M.D., F.R.C.P.,

Consulting Physician to the Hospital for Consumption, Brompton. ,

PAGE

[iitroductory — External Influences—The Nervous System — The Senses and their Organs — ^Profes- sions and Callings— Relief in Variety of Brain Work— Mental Strain— Retirement from Business— Life in Town and Country— Sleep— Dreams — Causes and Preventers of Sleep — Sleep-promoting Drugs— The Health of the Community— Sewage Arrangements— The State of the Public Health — Intemperance — Employment of "Women — Competitive Examinations — The Practical Rules of Health '. 519

TEAYELLING: ITS INFLUENCE ON HEALTH.

By J. Russell Reynolds, M.D., F.R.S.,

Consulting Physician to University College Hospital.

Travelling in its Relation to Time — Occasional and Habitual Travelling — Travelling in its Relation to Motive— The Duration of Travelling : Time and Space— The Character and Mode of Travelling— Walking— Running— Swimming— Bicycling and Tricycling— Riding and Driving —Rowing and Sailing— Skating and Ballooning— Railway Travelling— The Accompaniments or Concomitants of Travelling 559

HEALTH AT HOME.

By Shirley F. Mtjephy, Medical Officer of Health to St. Pancras.

Relation of Health to Home Conditions— Situation of the House— Soil— Construction and Arrangement of the House — Prevention of Dampness — ^Walls, Chimneys, Roofs, and Floors — Rooms and Furniture — Water Supplj'- Storage of Water — Filtration of Water — Disposal of Refuse — Faulty Drains and Disease — Drain Ventilation — Cesspools— Dry Methods of Disposal * — House-dust — Ventilation and Warming — Lighting — Artificial Light — Necessity for Cleanli- v ness — Sickness in the Home 589

HEALTH IN INFANCY AND CHILDHOOD.

By W. B. Cheadle, M.D., F.R.C.P.,

Physician to the Hospital for SicTc Children, Great Ormond St., and to St. Mary's Hospital. Capabilities and Progress of the Young Organism — Conditions influencing Development — Food and Feeding — Automatic Action of the Body — Materials Required for Use in the Body — Substitutes for Mother's Milk— Artificial Foods— Alcoholic Stimulants— Air and Light— y Exercise and Rest— Clothing— Washing and Bathing— Development— Its Stages and Dis- V orders — General Management of Childish Ailments 031

X CONTENTS,

HEALTH AT SCHOOL.

By Clement Dukes, M.D., B.S.,

Phynouin io Eugby School and to Rugby Hospital.

PACE

Introductory— School Health— Choice of a School— Choice of a Master— Choice of a Boarding- hoiuie— Education before Entering School — Sanitary Education— Entering School — Medical Examination — The Master's Boarding-house— Studies — Sleep— Dormitories— Meals— Sanitary Arrangements — School — The Chapel— Class-rooms — Over-work— School Government- Punish- ments— Play — Physical Education — Illness— Sick -houses — Epidemics and their Prevention — Infection— Self -regulation of Health — Day Scholars— Girls' Schools— Conclusion G77

THE EYE AND SIGHT.

By Henry Power, M.B., F.R.C.S.,

Ophthalmic Suvrgeon to St. Bartholomew's Hospital.

The Value of Good Eyesight— Structure of the Eye— ^Functions of the Eye — ^Power of Accommo- dation— Presbyopia— Acuteness of Vision — The Field of Vision — Colour - Blindness— The Effects of Variations of Light and Temperature — The Care of the Eye in Infancy — Purulent Ophthalmia— Long-sightedness, or Hypermetropia, and the Prevention of Squint — Myopio, or Short-sightedness — Ulcer of the Cornea — The Care of the Eye in Middle Age — Injurious In- fluences of Tobacco— The Preservation of the Sight— Nature and Prevention of Cataract- Protective Apparatus of the Eye 727

THE EAR AND HEAEING.

By George P. Field,

Av/ral Surgeon to St. Mary's Hospital. Anatomy of the Ear— Physiology of Hearing— How we Hear- Disadvantages of Impairment of Hearing— Rules for the Guidance of those who are Partially Deaf— Catching Cold in the Head— Deafness in Children— Injury from Bathing or Diving, and from Artillery Practice- Foreign Bodies in the Ear— Singing in the Ears— Scarlet Fever— Discharges from the Ear —Perforation of the Drum-head— Boxing the Ears— Nervous Deafness —Deaf Mutes— Aids to Hearing ^.gg

THE THEOAT, VOICE, AND SPEECH.

By John S. Bristowe, M. D., F.R.S.,

Senior Physician to St. Thornas's Hospital. /htroduction-Structure of Nose ; of Mouth ; of Throat ; of Larynx-Function connected with L^igestion Respiration, Voice, Speech -Functional Derangements connected with Mucous Surface, Chewing and SwaUowing, Paralysis. Spasm-Affections of Respiration; of Voice; of Speech-Defective Articulation-Stammering-Blundering Enunciation-Forgetfulness of liames-Hmts as to Public Speaking and Singing-Catarrh-Accidents to be Avoided

811

CONTENTS. xi

THE TEETH.

By Charles S. Tomes, F.R.S.

I'AGE

introductory— The Causes of Dental Caries— Defective Teeth— Overcrowding, &c.— Filling or Stopping— Gum-boils— Toothache and Neuralgia— Accidents to the Teeth— Premature Loosen- ing—Care of Teeth in Childhood 853

THE SKIN AND HAIE.

By Malcolm Mobbis, F.R.C.S., Ed.,

Surgeon to the Skin Department of St. Mary's Hospital. Structure of the Skin— Functions of the Skin— Baths and Bathing— Cold Bath— Hot Bath- Soap— Turkish Bath— Conditions that Influence the Health of the Skin— Poisonous Dyes in Clothing— Cosmetics— Hair in History— Structure of Hair— Management of the Hair- Bald- ness— Hair-dyes— Nails

HEALTH IN INDIA.

By Sib Joseph Fayrer, K.C.S,I., M.D., F.R.S., and Joseph Ewart, M.D., F.K.C.P.

Introductory— Routes— Best Time to Arrive in India— Best Time for Invalids a'nd others to Leave India — Travelling— Sport, or Shikar— Clothing — Punkah, Tattie, Thermantidote — Bathing — Dwelling-houses — Food and Drink— Drinking Water — Purification of Drinking Water — Siesta or Mid-day Sleep— Shampooing or Massage — Exercise — Smoking — Meteor- ology— Hygienic and Sanitary Divisions — The Hills — Terai— The Seasons — Influence of Sun and Heat — Prickly Heat — Febricula — Ague — Enlargement of Spleen — Anaemia — Remittent Fever — Typhoid or Enteric Fever — Sunstroke, Heatstroke, or Insolation — Effects of the Climate on European Women— Age at which Children should be sent to Europe— Poisonous Snakes, Scorpions, Centipedes, IMosquitoes, Land Leeches — Ticks — Bugs — Fleas 913

CLIMATE AND HEALTH-EESOETS.

By Hebmann Weber, M.D., F.R.C.P. Lond., Physician to the German Hospital. Causes of Climates — Constituents of Climate — Chemical Composition of the Air — Temperature — Humidity — Atmospheric Pressure— Light and Transparency — Electrical Conditions — Circu- lation of the Atmosphere — General Considerations — Division of Climates — Humid Marine Climates — Marine Climates with Mean Humidity — Winter Resorts on the British Coasts — British Summer Resorts— Dry Marine Climates — Inland Climates— Mountain Climates— Low- land or Plain Climates— Selection of Climates and Health-Resorts— Uses of the Home Climate 959

The Book of Health.

INTEODUCTOEY.

By W. S. Savory, F.RS., Surgeon to St. Bartholomew's Hospital.

Life and Health— The Organic Functions— Digestion— Absorption— Circulation of the Blood- Action of the Heart— Pulmonary Circulation— Respiration— The Animal Functions— The Skeleton— Muscular and Nervous Systems— The Brain- Vital Sympathy— The Distinctive Features op Life— Waste and Repair— Sleep— Dreaming and Somnambulism— Day-Dreams —Rhythmical Action— The I^L\.terial Agents op Vital Action— Food and Air— The Relation OP Physical Forces to Vital Action— Death— The Signs of Death — Health— Conditions Affecting Health— Man's Place in Nature.

No inquiry is so common everywliere as that which has reference to one's health, and such salutation is natural, for good health is not only the prime condition for the use and enjoyment of present life, but it is also full of promise for the future. But although Life and Health are among our most familiar words, and in their ordinary meaning none are more widely understood, yet in their scientific sense no terms are more difficult to comprehend.

Life constitutes the grand distinction between the organised kingdom, including all plants and animals on the one hand, and the inorganic or mineral kingdom on the other. Apart from life the several lines of demarcation in structure and compo- sition which have been from time to time laid down have been effaced as science in its progress has either swept away errors or revealed truths. It is true that the marks of difference are obvious enough in many cases, and in the majority, when collectively applied, are sufficient to solve any temporary difficulty that may occur ; but most of them disappear, and the others are by no means conclusive, when applied to the simplest forms. Now the features under which Life appears are infinitely varied — various in form and in expression, varying extremely too, from absolute simplicity to the most elaborate complexity.

Let us glance at the phenomena of Life in ourselves. How many and diverse are the actions or functions which minister to it ! There is digestion — a process for reducing food to a state of solution ; absorption — a process for conveying it when so dissolved into the blood ; the circulation — by which, as blood, it is conveyed all over the body to nourish it ; respiration — for introducing oxygen to combine with the elements of the food and tissues, and at the same time to carry off one of the chief and most poisonous of the products of that combustion, carbonic acid ; there are also the processes of secretion and excretion. There are extensive and intricate systems of organs for motion, the musclee j another, in its higher relations, ' 1

2 INTRODUCTORY.

more mysterious than all, the nervous system, for sensation ; for consciousness, thought, and volition, the instrument of mind.

Now if we extend our view we shall see the same functions at play in the animals around us. Life in them presents the same features. Their vital actions are like ours. Digestion, absorption, circulation, respiration, motion, and sensation are accomplished in them as in us. And this resemblance is not confined to the higher animals only, but it may be extended far and wide into the animal kingdom. Nay, it does not altogether stop here. Plants are living beings and their life pre- sents phenomena comparable with those of our own. However vague and far- fetched a comparison between the vital actions of plants and animals may at first sight or to superficial observation seem, the more thoroughly t'Re subject is investigated the closer does the resemblance appear. The difierences which are so obvious are of d^ree rather than of kind, and mask the similarity of their essential features. Plants require and take in food and air as we do, and circulate them through the system.

Heretofore the functions of motion and sensation were emphatically termed animal ones, on the assumption that they were absent in plants ; and were thus distinguished from the others, digestion, circulation, respiration, and the rest which, as plants have long been known to possess them in common with animals, were therefore termed vegetative. But while it has been long understood that many of the simplest forms of animal life yield very little evidence of motion and still less of sensation, recent researches have gone far to show that certain movements in plants are due to contractile tissue as in animals, and to render it doubtful whether one is justified in denying altogether what may be properly termed sensation to all plants.

To establish this relation and community of function between man and the creatures aroimd him, and between the animal and vegetable kingdoms, is a great step onward. The life of man, although a most intricate, is not an isolated problem, and its solution may be approached through the study of questions set in simple terms. But before proceeding further, let us review the several functions which together make up the life of the human body.

TJie Organic Functioiis, or the Functions of Vegetative Life. — The object of Digestion is to reduce the various substances used as food to a state of solution or minute division, so that they may be absorbed and carried into the blood. This is eflfected partly by mechanical and partly by chemical action. The digestive ap- paratus is of very elaborate construction. It consists of a long tube which extends throughout the body, and which is dilated at intervals into more or less capacious reservoirs. It commences at the mouth, to which succeeds a funnel-shaped cavity called the pharynx, leading into the gullet. This is a straight tube, which conducts directly downwards to the stomach, the most capacious portion of the whole alimentary canal, and capable, when distended, of containing about five pints. At the further extremity of this the small intestines commence. These consist of a convoluted tube some twenty feet in length, which occupies the greater part of the cavity of the abdomen, and at length terminates suddenly in a tube of larger calibre, the large intestine, some six feet in length, the last portion of the alimentary canal.

The whole of this long tube is lined with a soft, delicate membrane, very richly supplied with fine blood-vessels ; and on the outside of this the wall of the tube is

DIGESTION OF FOOD. 3

chiefly composed of muscle, by the contraction of which its contents are propelled onward. Into this tube numerous glands open and discharge their contents. In the very substance of different portions of the tube- wall itself minute glands are crowded in countless numbers, and at intervals, through longer and larger ducts, the secretions of the principal glands find their way into the canal, to mingle with its contents. Thus into the cavity of the mouth the salivary gland's pour the saliva ; into the intestines, a few inches below the stomach, the liver pours the bile, and the pancreas its secretion.

When food is introduced into the mouth, it is masticated, ground by the teeth, and mixed with abundance of saliva. The presence of food in the mouth, through certain nerves, excites the salivary glands to the formation of saliva, and this then flows freely into the mouth. The food is thus broken up, softened, and reduced to pulp. In this condition, by the action of the tongue and cheeks, it is formed into a bolus, and lodged on the surface of the tongue ; by the pressure of this organ upward against the palate the food is carried backward through the fauces or passage into the pharynx, where it falls within the grasp of the muscular wall of the tube, and is conveyed into the stomach.

It may be well to pause here for a moment to notice an exquisite arrangement for the protection of the air-passages from the ingress of food. The windpipe opens above, through the larynx, into the front part of the pharynx, just behind the tongue. All food, as it is swallowed, has to pass by this aperture, and a choking fit would be the constant result if any of it passed the " wrong way." To prevent this, imme- diately in front of the aperture of the glottis, a firm elastic tongue-shaped structure, called the epiglottis, stands more or less upright. Food, as it is carried backward, impinges against this, and either glides off on one side or passes over it and bends it backward, as a lid, over the aperture. Furthermore, the aperture itself is guarded by most sensitive muscles, which, on the hint of the slightest irritation, can close it completely by approximating its sides ; and lastly, in the movement of swallowing, the whole structure is drawn forward and upward, and the aperture itself becomes more vertical, so that all risk of intrusion is considerably diminished.

While in the mouth, food is not only reduced in consistence, but certain sub- stances in it undergo important changes from the action of the saliva. Soluble sub- stances, such as common salt, are at once dissolved, and this rapid and direct solu- tion is an important condition of taste and flavour. Starch, which is so abundant in certain kinds of food, as bread and potatoes, is acted on chemically, and converted into grape-sugar. jSTot the whole of the starch taken is thus changed by the saliva in the mouth, for the quantity supplied is probably too limited, and the time allowed is certainly too short, for the complete conversion of all that is taken; but the change begun in the mouth is continued to some extent in the stomach, until the action of the alkaline saliva is overpowered by the acid juice of the stomach itself, and it is subsequently resumed by the action of other agents in the small intestine. Food is swallowed by a muscular act. It does not fall passively into the stomach ; but is forced along by the contraction of the tube from above downward. Even liquids, as water, are thus conveyed. Thus a person may swallow food and drink in any position, even when upside down.

When food has passed into the stomach it is subjected to most important changes.

4 INTRODUCTORY.

When excited by the presence of food there, innumerable small glands, set in the walls of the stomach, pour out, in great abundance, a clear watery fluid, strongly acid, called gastric juice, which not only dissolves, as water would do, all soluble substances which have escaped the action of the saliva, but which has also a remark- able solvent action of a chemical kind on some of the chief constituents of the food, on tliose out of which subsequently 'flesh is formed, which are called albuminous principles. These are at once attacked by the gastric juice ; are softened, disinte- gi-ated, and dissolved. But they are not merely dissolved. They are at the same time somewhat changed in their constitution, and so rendered more fit for absorp- tion. This change and solution of the albumens by the gastric juice, like the change of starch into grape-sugar by the saliva, seems to be a purely chemical one, for it may be effected out of the body when these substances are mixed with the fluid. Nay, even a fluid resembling in this respect the natural gastric juice may be artificially prepared by soaking portions of the membrane of the stomach in water, and adding to the solution a few drops of hydrochloric acid. It appears that the quantity of gastric juice secreted by the stomach is enormous. It amounts pro- bably, on an average, to many pints : from ten to twenty daily. Considering the total quantity of blood in the body to be about fourteen pints, it would be impossible to undei-stand how this quantity of fluid could be drawn ofi* from it, except for the fact that it is being continually absorbed back into the blood, soon after its escape, c^rged with the substances it has dissolved ; so that, although so large a quantity is in the course of hours formed, at no given time does the stomach contain more than a few ounces of gastric juice.

During the whole period that the food is in the stomach the action of the gastric juice upon its contents is assisted by constant movement, due to contraction of the muscular walls. The food is thus churned, as it were, whereby every part of it is more thoroughly exposed to the action of the juice. The solution of successive por- tions is still further facilitated by the removal, through absorption, of that already dissolved ; so that at length what remains consists chiefly of oleaginous substances, such as fat, of some starch not yet fully converted into sugar, and of other sub- stances which are indigestible. All this is reduced to a tolerably uniform consis- tence, something like gruel, which, under the name of chyme, is passed onward into the commencement of the small intestine.

Here the chyme, which has an acid reaction when it leaves the stomach, soon imdergoes important changes. The bile' and pancreatic juice are mingled with it, and its reaction then becomes faintly alkaline. The oleaginous matter of the food — the fat, already in a state of disintegration — is now still further broken up into extremely minute particles. In fact, it is reduced very much to the condition of an emulsion, and in this form it is capable of being absorbed by certain structures in the wall of the intestine, presently to be spoken of. The fat, in the condition just described, appears among the other constituents of the chyme as a white opaque fluid, very like cream, and called chyle. What remains of starch in the food is con- verted into sugar, chiefly by the action of the pancreatic juice, which resembles that of the saliva. The small intestine propels its contents onward. All substances in a state of solution, and the chyle, are gradually removed by absorption, and

ABSORPTION OF FOOD. 5

some part of what remains is still further acted on by a juice which is poured out from minute glands in the wall of the intestine, and made soluble. At length the residue is carried into the large intestine, and this, consisting mainly of indigestible matter, substances which have resisted the action of the various solvents to which they have been exposed, of the remains of the several secretions which have acted on the food, and of some matters which- have been thrown into the canal as excrementitious by the agency of some of its glands, is cast out.

The process of Absorption — the means whereby digested food is passed into the blood — follows that of digestion. This is very largely accomplished by the minute blood-vessels themselves. Their walls are composed of a very thin delicate mem- brane, which readily allows of the passage of fluid through them, and such a passage is greatly promoted by the current within. These vessels, which, as already mentioned, are most richly supplied throughout to the mucous membrane that lines the alimentary canal, absorb at once the several substances that are in a state of complete solution, and the fluids which have acted on them. Thus the gastric juice, charged with the albuminous substances it has dissolved, is absorbed, so also is the soluble grape sugar into which the saliva has converted the starch ; but the fats, the oleaginous substances of the food, are not thus absorbed by the blood- vessels. Although, as already explained, they are reduced to a state of very minute division, even to an emulsion, yet they are not actually in solution, and so they find their way into the blood through other channels.

The surface of the mucous membrane of the small intestine may be seen, with the microscope, to be studded all over with minute conical eminences, called villi. These, which exist in enormous number — as many as from forty to ninety being counted in a square line — are constructed after the fashion of the mucous membrane from which they spring ; but in the interior of each villus is the commencement of a single vessel, or minute cluster of vessels, which does not contain blood, but whose office is to absorb the chyle. Hence, from the appearance of this milk-like fluid these vessels are called lacteals. These lacteals, which begin in the villi, pass in great number from the wall of the intestine to a common trunk, which commences in front of the spine, in the loins, and runs upward to the left side of the neck, behind the collar-bone, where it discharges its contents into one of the great veins, where, of course, the chyle mingles with the blood.

So of the products of digestion, one part, that which is forthwith reduced to a state of perfect solution, finds its way at once through the walls of the blood-vessels into the blood, and this is conveyed by the arrangement of the vessels that absorb it at once to the liver, where it is subjected to changes, which result in bringing it into closer relation with the blood ; the other part, which is converted into chyle, finds its way to the blood, not at once, but only indirectly, through an extensive system of vessels, the lacteals. Now, during the passage of the chyle through the lacteals it undergoes important changes, and these changes, which result in transforming the chyle into a fluid much more closely resembling the blood, are chiefly eflected by the agency of certain bodies through which the lacteals pass in their course. These bodies, or glands, which in size and shape may be likened to small almonds, are very numerously set in the path of the lacteals.

« INTRODUCTORY.

But this remarkable system of vessels, wliich in man and the higher animals stauds, as it wert?, between the materials that it absorbs and the blood into which these materials are at length cast, is not confined to the alimentary canal. Vessels of a like kind are distributed all over the botly, and are found abundantly in some of the tissues, but they are f6r the most part so fine and delicate that they are apt to escape observation in an ordinary dissection. Those which are distributed over the body generally, of course, cannot contain chyle, for this is only formed in the small intestine as the immediate product of digestion, but these contain a transparent, colourless fluid, called lymph, and hence these vessels, in distinction to the lacteals, are called lymphatics. The immediate source of this lymph and the conditions under which it is formed are not yet clearly and fully understood. In fact, the exact mode in which the lymphatic vessels commence in the tissues, and their relation there to the blood-vessels proper, has not yet been quite satisfactorily made out ; so the questions, how far lymph is from blood, and to what extent it may be regarded as an excrementitious product, are still open ones. But that this lymph is very far from consisting entirely, or even principally, of refuse matters ; on the contrary, that it must play some future part of importance in the economy, would appear from the fact that it finds its way into the blood after passing through lymphatic glands, and that before it arrives there much of it is allowed to mingle with the chyle in a common vessel.

Thus, by digestion and through absorption, the materials of our food find their way into the blood. They do not reach the blood as blood, but after they have entered the current of the circulation they have to be still further elaborated. The final steps of the change, at all events, must be accomplished in the blood itself. Thus the fluid of the blood is crowded with myriads of microscopic bodies, called blood-cells. These are of two kinds, known respectively as the white and red blood- cells. The proportion of these varies, but the red are always in excess of the white. Cells resembling the white blood-cells, and which are gradually converted into them — in short, young blood-cells — are found in chyle and lymph in greater abundance and more fully formed as these fluids, in their course towards it, approach the blood ; but the red blood-cells are not found in them ; they exist only in the blood itself, and to them its characteristic colour is due. The blood, although the common source of supply to every part, and although constantly replenished by the crude material which it has to make into the likeness of its own substance, nevertheless maintains its condition. The great mass of it is uniform in structure and com- position. It possesses, then, the characteristic attributes of vitality — it is a living fluid. The blood itself has life.

The fluid portion of the blood, called liquor sanguinis, or plasma, consists of various substances held by water in solution, organic compounds of difierent groups, albumens and hydro-carbons, and various inorganic salts. The red cells play a conspicuous part in the purification of the blood by the function of respiration, and this by virtue of their especial affinity for oxygen. The white cells, out of which the red are formed, have of late years attracted particular interest, from the discovery that they are capable of spontaneous movement. While alive, they may be seen, under the microscope, to change their form, to throw out processes and to

CIRCULATION OF THE BLOOD. 7

retract them ; in short, to behave as simple fragments of living protoplasm will do in other circumstances, as in vegetable tissue and the lower forms of animal life. These cells, too, can escape through the walls of the finest blood-vessels without rupture, and wander far and wide into the tissues.

But in order that the blood may be enabled to fulfil its high offices it must be brought into relation with the several structures of the body : it must circulate; and the Circulation of the blood is provided for by an elaborate apparatus, the ex- quisite mechanism of which never fails to excite the wonder of all who study it.

The various structures of the body are traversed by a net-work of very fine and delicate vessels, called capillaries, the walls of which are transparent and permeable, so as to allow of transmission and active interchange between the blood which flows through them and the tissues in the midst of which they are placed. It is through these capillaries that the several structures are nourished, that they receive from the blood the materials of supply, and return to it the products of their waste. The closeness of this net-work of vessels, or, in other words, the supjjly of blood, varies very widely. Some structures, as the skin and the muscles, are highly vascular, and contrast strongly with the bones and ligaments. The blood is brought to these capillaries from the heart which propels it, by the arteries, which form a system of pipes laid down in every direction for the purpose, and it is returned from the capil- " laries to the heart by the veins, another system of pipes, which, for the most part, run in company Avith the arteries. Thus the blood circulates. It starts with a rush from the heart by the force of its action; passes along the arteries everywhere to the capillaries ; through the capillaries it performs its great office of noiTrishing the body, and then by the veins finds its way back again to the heart. The blood, then, in its circulation through the capillaries, must undergo great changes, for it gives up part of its substance and of its oxygen, and receives in exchange refuse matters, and becomes charged with carbonic acid gas. Thus arterial blood differs from venous blood in composition and in colour. Arterial blood is of a bright scarlet hue, and venous blood of a dark purple ; and the contrast in colour is in general so striking, that when a person is bleeding one can usually tell, if either an artery or a vein be wounded, from which vessel the blood flows.

After the blood, then, has circulated through the tissues, it is in a measure spoiled for further use, so when it returns to the heart as impure blood, it must be restored before it can be again sent forth. This is largely accomplished by its passage through the lungs ; so when the blood arrives at the heart after nourishing the system, it is transmitted to the lungs to be purified by the act of respiration, and then returns to the heart fit again for its work. No portion of the blood, therefore, finds its way twice through the system without meanwhile having passed through the lungs. In the lungs, as will be presently explained, it receives fresh oxygen and gives off" car- bonic acid, and it is changed there from venous to arterial. Thus there are two chief circulations in the body : one called systemic, during which the blood is changed from arterial to venous, sometimes styled the greater circulation ; and one called pulmonic — the lesser circulation — by which venous blood is changed into arterial; and every portion of the blood is subjected alternately to these two processes.

The great agent in the circulation of the blood is the heart, which, in relation to

8 INTRODUCTORY.

its office, is a double organ. One half of it, the left, drives the blood through the system ; the other half of it, the right, drives the blood through the lungs. Let us look at its action somewhat more closely. The heart is substantially a powerful nmscle. The blood is received into cavities in the interior, and is propelled there- from by the energetic contraction of their walls, which squeeze it out into the arteries. The two sides are constructed upon the same plan, have about an equal capacity, and work in the same way ; only that the wall on the left side is much thicker and stronger than on the right, because it has more work to do. The two cavities with these muscular walls are called ventricles, and receive the blood, the one from the ^stenif the other from the lungs. But the ventricles do not receive the blood directly from the veins. It ffows to the heart from the veins into two ante-chambers, called auricles, which pass it on to their respective ventricles. The auricles, which have a capacity almost or quite equal to that of the ventricles, have also 'muscular walls ; but these are far thinner than those of the ventricles, so that, when empty, the auricles appear as insignificant structures set upon the ventricles, which remain firm and preserve their shape, so familiar to us as a standard of comparison. The function of the auricle is in direct relation to that of the ventricle. If there were no auricle or ante-chamber intervening, the blood would have to find its way into the ventricle from the large veins more gradually ; but as it is, it accumulates in the auricle from the veins, as in a reservoir, and then is at once and abruptly trans- mitted to the ventricle, which it fills, and which then contracts and sends it outward.

So, then, th'e human heart has four cavities — two ventricles and two auricles ; on each side a ventricle and an auricle. Each auricle communicates directly with its ventricle, but between the two sides there is no direct communication. They are bound together in one organ, they work together, act synchronously ; but in their offices they are distinct.

The course of the blood through the heart and the plan of its circulation may now be understood. Starting from the left ventricle, it is driven over the body, through the arteries, into capillaries, and onward to the veins. By them it is re- turned to the right auricle, which transmits it to the right ventricle. The right ven- tricle drives it through the arteries to the capillaries of the lungs, and onward into the veins, which return it to the left auricle, and this transmits it to the left ventricle, whence it starts again to the system.

And it is well to pause here for a moment to observe the means by which its onward course is secured, and regurgitation of, or confusion in, the current pre- vented. The construction is so simple, and its purpose so obvious, that it may be easily understood, and the interest of it is enhanced by the fact that precisely the same kind of mechanism is employed in various ways in the construction of different kinds of instruments. Every one understands the principle of action of a flood-gate ; every one knows how these are employed in the construction of the locks on our rivers; every one can explain, too, the purpose for which valves are introduced into pumps and syringes, and their mode of action. When water is driven in the required direc- tion, they are opened, and offer no hindrance to its flow ; but when it would regurgi- tate, the backward pressure closes them, and not a drop can pass. In the heart there are such valves, only singular in the exquisite deHcacy of their finish and the per-

ACTION OF THE HEART. 9

fection of their action. Each ventricle has two orifices : one through which the blood flows in from the auricle, another through which it flows out into the artery. Each of these orifices is guarded by valves, which difler in shape and other details of con- struction, but which work in the same way. When the ventricle contracts and expels its blood, the orifice which leads back into the auricle is closed by the valve there, and so blood can find its way only onward into the artery. When the ventricle ceases to act, the distended artery, recoiling on the blood, closes its valve, and so no blood can return to the ventricle.

Each action of the heart, in a healthy adult, occupies something less than a second of time. About half of this is taken up by the contraction of the powerful ventricles by which the blood is driven into the arteries; during the other half the ventricles are dilating and re-filling. The contraction of the auricles, which immediately precedes that of the ventricles, is more sudden, and occupies only one- eighth of the whole period. During the remaining seven-eighths they are gradually being re-filled. The contraction of the ventricles causes the beat of the heart, for by their action the heart is not only altered in size and shape, but, owing to the spiral arrangement of the muscle, it is vigorously moved. The front of it is tilted upward with a slight curve to immediately behind a particular portion of the wall of the chest on the left side, just below the fifth rib, where this stroke or impulse, as it is called, can usually be felt. Moreover, by the beating of the heart certain sounds are produced, which can be heard when an ear is placed over its region. Two sounds, differing in length and character, can be detected, followed by an in- terval of silence. The first sound is the longest and dullest, and. is synchronous with the impulse or stroke of the ventricles, and is probably due to the closure of the valves between the auricles and ventricles. The second sound, which imme- diately succeeds, is shorter and more abrupt, and is certainly due to the closure of the valves between the ventricles and great arteries.

The arteries, which ramify all over the body to conduct blood to the tissues, in their arrangement may be compared to the stem and branches of a tree. The great trunk, which starts from the left ventricle, gives off" branches in its course. These divide and sub-divide as they pass outward, becoming more numerous and much smaller, until they gradually end in the capillaries. When an artery divides, the united area of the branches generally exceeds the area of the trunk, so that the total capacity of the arterial system greatly increases as it becomes more distant from the heart. Where the arteries join the capillaries their total capacity is something like eight hundred times greater than the capacity of the first vessel at its origin from the heart.

The arteries are not rigid and merely passive tubes, but besides being very strong, possess two properties which are quite distinct, one physical, and the other vital. They are eminently elastic, capable of expansion and extension, and of recoil when the force which stretches them is withdrawn. This may be easily shown after death, when an artery is removed from the body, for the property is a physical one. The elasticity of the artery plays an important part in the movement of the blood. If the arteries were rigid and unyielding tubes, a considerable portion of the heart's force would be uselessly expended against their walls ; but as it is, they yield and

10 INTRODUCTORY.

are distended by the blood which is driven into them, and then in turn recoiling on their contents, force the blood onward in the direction that it should go, for the valve at the commencement prevents its return. Thus successive waves of disten- sion are carried along the arteries from within outward, each one being due to a beat of the heart, and these waves can be detected by the finger whenever it is placed on an artery large enough and superficial enough to be felt, as at the wrist, where they are recognised as the pulse.

Tliis intermittent movement of the blood through the arteries is strikingly shown in the maimer in which they bleed when wounded. When an artery is cut across, the blood spurts out with great force to a distance of several^ feet ; but the flow is not continuous. It escapes in a series of jets, the long, slender scarlet stream rising and falling with each beat of the heart, and this pulsation of the blood stream tells at once that it comes from a woimded artery.

But as the blood traverses these elastic tubes the abruptness of the heart's stroke becomes gradually broken and the current equalised ; so that the greater the distance from the heart the less obvious is the pulsation, until at length in the capillaries the rate of the stream becomes uniform.

But the arteries are not only elastic ; they possess the vital property of contrac- tility, and this is due to very delicate fibres of muscle in their wall. The arteries are not uniformly endowed in this respect ; as a rule, this muscular power increases as the arteries become smaller. Those towards the capillaries are the most contrac- tile. This property serves them in more than one way. By affecting their calibre, it enables the arteries in great measure to become adjusted to the amount of blood they contain- By wtue of the elasticity already noticed, they can expand, and consequently contract ; but the expansion, which is due to their elasticity, must depend on the pressure of the blood within them. It is a passive state. But their vital contractility is an active one, and by it they are enabled, within limits, to regulate the size of the stream ; that is, the quantity of blood which passes through them. Thus the amount of blood that they distribute to any particular organ is by no means invariable. It is determined by the wants of the part itself. When an organ is in active operation, it requires and obtains more ; when comparatively quiescent, it neieds and receives less. This adjustment of supply and demand is effected through a portion of the nervous system, which establishes a communication between the part to be supplied and the arteries which supply it, and these can respond to the signal they receive by virtue of their muscular tissues.

The veins form a system of vessels which in general arrangement may be roughly compared to that of the arteries. They commence from the capillaries, and gradually uniting, form fewer and larger trunks as they proceed onward to the heart. The total area of the venous system — ^that is, its capacity — is at least twice as great as that of the arterial ; and moreover, the veins, although their walls are composed of structures similar to those in the arteries, possess them in difierent proportion and yield more readily to the pressure of the blood. Hence, when from any cause the flow of blood through them is obstructed the veins swell largely, and the super- ficial ones stand out prominently under the skin. Most of the veins, especially those that lie amongst the muscles, contain at intervals valves in their interior, which

PULMONARY CIRCULATION OF THE BLOOD. U

prevent the regurgitation of the blood ; for by the time the blood reaches the veins the greater portion of the heart's force has been expended, and it returns in an equable and comparatively languid stream.

Now, the relation of the several parts to each other of this elaborate vascular apparatus must be clearly understood. The work of the blood is carried out in the capillaries ; the heart, arteries, and veins constitute simply an apparatus for the appropriate distribution of the blood. Although the capillaries are such minute vessels, and although the length of capillary structure that any given portion of the blood has to traverse may be measured for the most part by the fi:'action of an inch, yet they form such a vast net-work throughout the system that by far the greater part of the whole quantity of the blood in the body is contained in them. The amount altogether in the heart is only a few ounces, probably not more than four or five. The quantity in the large arteries and veins together would be but a small fraction of the whole. The great mass is always contained in the smallest vessels in the substance of the tissues ; and the rate of the blood current through the successive portions of the vascular circle must be inversely as their area. Thus the blood moves fastest in the arteries, perhaps at a rate of more than a foot in a second soon after it leaves the heart. Then as the capacity increases the rate diminishes, until in the capillaries the slender streams are hardly at the rate of two inches in a minute, and in the veins, again, not half so rapid as in the arteries.

Moreover, while in the capillaries the stream is most subject to variation. As already observed, the amount that passes through the same organ varies widely at different times, under different conditions ; but even in different portions of the same structure local variations may be constantly observed. As every one knows, the circulation of the blood may be seen in transparent parts, as, for instance, in the web of the frog's foot or of the bat's wing. As we watch it, the arterial stream of supply and the venous stream of return may be tolerably constant for hours, but between them, throughout the field of observation, the capillary circulation is sub- jected to frequent fluctuation. Now, one portion of the net-work is more distended than another ; sometimes a vessel here and there seems too small to admit the blood- cells even in a single file, and only fluid passes ; but, again, a cell or two make their way into it, and then others follow. And there can be little doubt that although the blood finds its way into the capillaries, and through them by the force of the heart's action, yet while in the capillaries it is subjected to other influences which largely affect its flow ; and these depend on the changes which therein take place. When these changes are normal and free the capillary circulation is promoted by attrac- tions between the tissues and the blood ; when they are obstructed, the capillary circulation is obstructed too. This great fact lies at the root of the mischief which is observed in inflammation and in other morbid processes.

The pulmonary, or lesser, circulation has been already alluded to : the effect of which is to send the blood that has been rendered impure during its passage through the tissues to the lungs, so that it may be purified by the act of Respiration.

The two lungs occupy the greater portion of the cavity of the chest. They are highly elastic, sponge-like structures, in the substance of which the blood and air are brought together. In its simplest form, as it appears in some of . the lower

12 INTRO D UCTOR Y.

animals, the lung is a sac, the wall of which is composed of a very delicate trans- parent membrane. On this wall is distributed a net-work of fine capillaries, and the cavity in the interior is filled with air. Through the delicate membrane, which is the only structure that intervenes between the blood and the air, oxygen freely passes from the air into the blood, while the carbonic acid gas from the blood freely passes into the cavity and mingles with the air. Thus respiration is carried on. The human lung, although a far more elaborate organ, is constructed upon the same plaiL The windpipe commences above, in a special organ called the larynx, in which the voice is produced, and which, as already mentioned, opens into the front part of the pharynx, at the base of the tongue. The -windpipe is continued downwards into the upper part of the chest, where it divides into two branches, one of which passes to each lung. These bronchial tubes divide and sub-divide throughout the substance of the lung after the fashion of the branches of a tree, and at length end in irregular cavities, around which, and opening in them, minute sacs, or air-cells, cluster in great numbers.

The windpipe and bronchial tubes have finn, stout walls, which are further strengthened by rings of cartilage, or gristle ; and they also contain muscular fibres, by which their capacity may, within certain limits, be adjusted, and which doubtless enables them to assist powerfidly in the expulsion of matter, such as phlegm, that may have to be from time to time dislodged. But the walls of the air-cells are composed of a very delicate membrane, and covered with a rich net-work of fine capillaries, through which, of course, blood sent from the right side of the heart is constantly flowing. It has been calculated that the human lung contains from five to six millions of these air-cells, the membrane of which, if spread out, would be equal to a plane surface of at least from ten to twenty square feet. The air which enters by the windpipe finds its way freely into the cells, and so comes into close relation with the blood. By the mechanism of respiration, fresh air is being continually drawn into the interior of the lungs, and that which has been used is expelled. Nowhere can the successive stages of progress of an organ, from its first condition, which is one of extreme simplicity, to its most elaborate state in the highest animals, be more clearly traced than in the lung : in its rudimentary form, a mere membrane be- tween the blood and the air ; then the extent of surface for exposure is increased by folds, either outward, in the form of gills, for aquatic respiration, or inward, as in lungs, for aerial respiration.

In man and the higher animals air is drawn into and expelled from the lungs by the movements of the chest. The cavity of the chest is everywhere closed to the admission of air, except through the windpipe, which leads into the lungs. If the cavity of the chest be enlarged, the additional space is forthwith occupied by aii*, which rushes into the lung, and its elastic structure expands. If the cavity be dimi- nished, the elastic lung contracts, and the air is expelled. In each case the lungs adapt themselves to the movement of the chest-walls. In inspiration, the chest is enlarged in every direction by powerful muscles. The chief muscle of inspiration forms the floor of the chest, and separates it from the cavity below. It is called the diaphragm. When relaxed, it is dome-shaped, and rises up into the cavity of the chest When it contracts, it descends, and becomes more nearly plane, and thus the

RESPIRATION. 13

space is deepened vertically. Between the ribs are muscles, whicli raise them, and thus enlarge the chest horizontally. When the force is relaxed, the chest-walls recoil by their elasticity; but this movement also is assisted by certain muscles attached to them. Thus each act of respiration consists of an inspiration, whereby the cavity of the chest is enlarged, so that air rushes in and the lungs expand, and of an expira- tion, whereby the chest- wall and lungs contract, and air is expelled. The respiratory movements are regular, like the pulse, but less frequent. They occur from fifteen to eighteen times in a minute.

The movements of respiration are very obvious. Every one is familiar with the rise and fall of the chest. But if this expansion of the chest-wall be carefully watched, a difference may be observed between men, women, and children. In men, the expansion is throughout more equable ; the chest enlarges considerably in every direction. In women, the movement of the upper portion of the chest-wall is more free in proportion to the lower. No doubt this deficiency of movement of the lower ribs in women is due in large measure to the mode of dress ; but even naturally it would appear that, in proportion to that of the lower ribs, the movement of the upper ribs is more free in women than in men. In children, the chief enlargement of the chest in inspiration is in the vertical direction, and due to the descent of the diaphragm ; so, when the respiration of a child is observed, the rise and fall of the abdomen, which alternate with the movements of the chest, is very marked, for as the diaphragm descends it presses upon the abdominal contents, and the walls yield.

In respiration, air is alternately drawn into and expelled from the lungs ; but the lungs are not completely emptied and re-filled by each act. Only a small frac- tion of the whole quantity of air in the lungs is each time changed. By an ordinary expiration, about 20 or 25 ciibic inches of air are expelled, and an equal quantity is drawn in by inspiration. After expiration there still remain about 200 cubic inches of air in the lungs. Even the most forcible expiration can only further expel about half of this, so that then there still remain about 100 cubic inches within. The most forcible inspiration can introduce about 100 extra cubic inches of air ; so that, in relation to, the capacity of the chest and the amount of air in the lungs, the proportiou changed by each act of ordinary respiration is very small : not more than one-eighth or one-tenth of the whole. The air which flows in and out in ordinary respiration is called tidal air ; that which remains after an ordinary expiration is called reserve air ; that which remains after the most forcible expiration is called residual air; and the excess which can be introduced by the most forcible inspiration is called complemental air. The maximum amount represents, of course, the capacity of the lungs. Even after death, when the lungs are removed from the body, they are very light and buoyant, owing to the quantity of air they contain ; nor can the w^hole of this air be driven out, even by very powerful compression.

Now, as the tidal air bears so small a proportion to the residual air, it becomes an interesting question how the air which remains in the lungs can be changed. This is efiected by a physical law — the law of diflfusion of gases. When two difierent gases are brought together, they diffuse into one another until they are thoroughly mixed. The rate of diffusion of different gases depends on their density ; the rate of diffusion

14 INTRODUCTORY.

of Rny gas is inversely as the square root of its density. So the fresh air from with- out diffuses into that whicli is within, and thus the change is constant.

The chiof change which occurs between the blood and the air in the lungs is that oxygen gas passes from the air into the blood, and carbonic acid gas passes out from the blood into the air. Both venous and arterial blood contain both oxygen and car- bonic acid, but in different proportion. In arterial blood there is in volume about 16 per cent, of oxygen and 30 per cent, of carbonic acid. In passing through the body, oxygen is gradually removed, and carbonic acid added, so that venous blood, when it flows to the lungs, contains about 6 per cent of oxygen and 35 per cent, of carbonic acid. Thus, in the lungs, about 10 per cent, of oxygen is added to the blood, and 5 per cent, of carbonic acid is given off.

The attraction of blood for oxygen is due to the red blood-cells, the substance of which holds oxygen in loose combination ; and it is mainly by the action of oxygen on the substance of these blood-cells that the colour of the blood is changed. Hence the red blood-cells have sometimes been styled oxygen-carriers.

But the introduction of oxygen and the escape of carbonic acid, although the chief, are not the sole changes that occur in respiration. Water from the blood is added to the air in the form of vapour, and is readily deposited when the warm breath is chilled by falling on a cold surface. The amount of water which is thus lost depends mainly on the amount which is already in the air. When air is expired it is saturated with watery vapour, and its capacity in this respect is determined by its temperature. Air inhaled at the ordinary temperature is warmed while in the lungs, and expired at a temperature of about 98° Fahr. Thus its capacity for watery vapour is increased. On an average, in twenty-four hours about ten ounces of water are thus carried off by respiration. Minute traces of organic, volatile, and some other substances, are also added to the air, and these are often revealed by the odour of the breath.

Atmospheric air is composed of a mixture of oxygen and nitrogen, in the propor- tion by volume of one to four. But even the purest air contains traces of other sub- stances, and the air we breathe is often by no means of the purest. Not only are traces of carbonic acid and ammonia found in it, but in many places of low situa- tion, especially in the neighbourhood of populous and manufacturing districts, various substances in a solid form are suspended in it. Smoke, for instance, often obviously abounds, and many persons are made painfully conscious of the effect of such im- purities in a London fog. Such substances, although foreign to the natural consti- tution of the atmosphere, are yet, when suspended in it, carried into the bronchial tubes, and would doubtless become the source of perpetual irritation but for an exquisite structure by which they are arrested before they reach the delicate air-cells, and carried back to the larger bronchial tubes, whence they may be expectorated. The surface of the whole mucous membrane of the pulmonary passages, from the lining of the nostrils to the smallest tubes which end in the spaces leading to the air-cells, is covered throughout by a layer of very minute hair-like filaments, called cilia. These fine hairs, which can be seen only by a high power of the microscope, are in perpetual motion, by which waves constantly flowing in a direction towards the outlet are produced. When this motion is witnessed, one is reminded of the effect of a current of wind over a field of ripe corn. But here the movement is an

THE LUNGS. 15

inherent one, and due to the action of a contractile substance. If, while we watch this action, we introduce into the neighbourhood of the cilia some particles of a finely-divided substance — as, for instance, of carbon, such as from smoke — we see that the instant they alight on the waves they are wafted onward. Thus the whole surface of this vast tract is being continually swept, and the products are often seen in the discoloration of the sputa. The air so sifted, and comparatively pure, finds its way to the pulmonary cells, and the oxygen through their walls to the blood.

Inasmuch as the whole of the blood has to flow alternately through the system and the lungs, it follows that in any given period as much blood must flow through the lungs as through the system. But the total capacity of the lungs for blood is much less than that of the system: perhaps not more than one-fifth; so that the rate of the pulmonary circulation must of course be proportionately faster. And it may be observed, too, that while everywhere else throughout the system the arteries carry bright blood, hence called arterial, and the veins dark blood, hence called venous, the pulmonary arteries carry dark venous blood to the lungs, and the pul- monary veins return bright arterial blood.

Venous blood in the lungs excites, through a certain portion of the nervous system, the muscles of inspiration. These respond ; and by their action enlarge the cavity of the chest, and thus air is introduced. In ordinary circumstances, during health, this process is continued without any consciousness of it, but it may never- theless be brought within the range of both consciousness and the will When atten- tion is directed to the movements of respiration, we become aware of them, and we may, to a certain limit, control them by the will. ISTay, by watching them, we dis- turb them. We only breathe quite naturally and regularly when the act excites no attention. By voluntary efibrt we may for a short time suspend the action alto- gether, but at length the want of breath, due to the accumulation of venous blood, becomes too strong for the will, and, in spite of the utmost resistance, we breathe again. The respiratory movements are peculiar in their relation to consciousness and to the will. Habitually beyond consciousness, we can nevertheless feel them, if we will. But it is only when the function is perfectly performed that it escapes atten- tion. Like other functions, but this in an especial degree, any hindrance to the process or embarrassment of the movements soon produce strong sensations, which rapidly rise into pain and agony. For if, from any cause, the blood cannot undergo due changes in the lungs, the pulmonary circulation is hindered. Venous blood accu- mulates, and vehemently excites the pulmonary nerves. The distress arising from want of breath grows stronger ; more powerful efforts are made by the muscles to introduce air. If relief be not obtained, the excitement and suffering are for awhile continued, until the increasing impurity and engorgement of blood in the nerve- centres deaden their sensibility. Then they fail in action, and death soon super- venes. Thus persons die when suffocated. At first there is a severe struggle for air; then convulsions and delirium, insensibility and death. And the prime cause of the mischief — the overcharge of the system with venous blood — is plainly revealed in the aspect of the sufferer, even for some time after death. The surface of the body, more particularly of certain parts of it, as the face, hands, and feet, becomes of a dusky livid colour, from the dark blood in the vessels of the skin ; and parts, such as the

16 INTRODUCTORY.

lips, which yield most readily to distension, become greatly swollen from engorge- ment In some forms of disease, which, as they advance, interfere with the great function of respiration, as various affections of the heart and lungs, the gradual pro- gress of these effects of defective aeration of the blood may be distinctly traced. At first, it may be, the patient suffers only from shortness of breath. He can breathe in comfort when calm and quiet; but excitement, or exertion, or any disturbance, is too much for liim, and he pants for want of breath. Then the extra demand cannot be adequately met by any effort, and when the circulation or respiration is at all disturbed the surface becomes dusky, and he is greatly distressed. At length, even when the needs of the system are reduced to the lowest degree by rest, and he is placed in the most favourable position, the blood is never fully aerated. The anguish increases imtil, as the blood grows more impure, the functions of the brain fail, and he passes through delirium and insensibility to death.

The action of the respiratory muscles is remarkable in that they may be aroused, not only as they are constantly, and always most strongly, by the lungs, but also by the skin. The relation between the surface of the body and the function of respira- tion through the nervous system is a very close one, and some striking instances of it must be familiar to all. A sudden plunge into very cold water is apt to produce temporary embarrassment, and although this might be perhaps partly explained by the contraction, consequent on cold, of the vessels of the skin, and a corresponding fulness of the deeper organs, yet that this cannot be the principal cause appears from the fact that a like result may be produced by certain impressions on a very limited portion of the surface. A cold douche upon the head, for instance, will often inter- rupt inspiration, and provoke for a moment or two disorderly action. A morsel of ice dropped down the back between the skin and clothes will disturb also the equanimity of the respiratory movements, and when flagging in faintness, they may often be aroused by dashing cold water on the face or chest, or by slapping the surface with a cold wet toweh No explanation of the acknowledged success of these domestic expedients is satisfactory which excludes the intervention of the nervous system.

Allusion has been already made to the means by which foreign matter is being constantly, but quietly, removed from the pulmonary passages; but these substances, as well as others which result from the secretion of the mucous membrane, are at times more forcibly expelled by a special modification of the respiratory act. Cough- ing consists first of a deep full inspiration, by which the lungs are filled with air. Then the glottis, or upper orifice of the windpipe, being completely closed, this is followed by a sudden and forcible expiration, which bursts open the glottis and drives out a blast of air. This peculiar action of the muscles concerned is provoked through the nervous system by some irritation in some part of the respiratory passages.

In sneezing, the same essential action occurs, except that, in this case, the com- munication between the mouth and pharynx is closed, so that the blast of air is driven entirely through the nose.

Hiccough is caused by a sudden inspiratory contraction of the diaphragm, during which the glottis abruptly closes, so that the further entrance of air is checked. The air about to enter strikes upon the closed glottis, and produces the well-known sound.

But owing to the relation in which the respiratory mechanism stands to the

EXCRETORY PROCESSES. 17

nervous system, its movements are, as we have already seen, very easily disturbed, and thus it becomes the instrument of expression in various emotions.

Laughter is produced by an inspiration, succeeded not by one only, but by several short spasmodic expirations, the glottis being freely open, and the vocal chords being thrown into characteristic vibrations.

In crying, the respiratory movements are modified in much the same way, and the two actions are frequently indistinguishable. The facial expression, however, is usually different. Sobbing is due to a series of convulsive inspirations.

A sigh is only a deep and long-drawn inspiration, followed by a somewhat shorter expiration.

In yawning, the inspiration is deeper and longer than in sighing, and the air is drawn, not through the nose, but through the widely-open mouth, the lower jaw being greatly depressed.

It has been mentioned that the windpipe is surmounted by a special structure, called the larynx, which opens into the front part of the pharynx, behind the base of the tongue, and through which all air in its ingress and egress passes. This is the organ of the Voice, and the various sounds which constitute it — the notes of which it is composed — are produced by the vibration of two more or less parallel and ex- quisitely elastic chords, the tension and degree of approximation of which are regu- lated by delicate muscles. The active agent in producing vibration of the chords is the current of air forced in expiration from the lungs. The voice is subsequently moulded by the tongue, lips, teeth, and adjacent parts, into language.

In the lungs, then, carbonic acid is removed from the blood, the chief product of the combustion or oxidation of the substance of the food and tissues. At the same time, fresh oxygen is introduced to the blood. Life depends very directly on both these conditions. If either be arrested, death soon follows. When both are hindered, as when persons die from want of breath, the effects produced are due to both causes. The carbonic acid unduly retained becomes an active poison, but perhaps the deficiency of oxygen is more directly concerned in the fatal result.

Another chief product of oxidation in the body is urea, which escapes by the kidneys. This substance largely contains nitrogen, and therefore represents the waste of flesh and of the nitrogenous or flesh-forming substances of food. Bather more than an ounce of urea is excreted daily.

The inorganic salts which are contained in food, and which enter into the compo- sition of the tissues, are carried off mainly by the kidneys, and to a less extent in the perspiration by the skin.

More water escapes by the skin as perspiration than by the lungs in the breath, but the proportion is very variable — from both sources, on an average, more than two pints daily. The greatest amount is drawn off by the kidneys — between two and three pints.

Carbonic acid, urea, inorganic salts, and water — these are the chief substances which have to be carried off from the body, and the means by which they are re- moved is called the process of excretion. Between the various substances taken as food for nourishment and these stand the blood and the several tissues of the body. The food is converted into blood, and some of it still further into tissue. Then, in

2

18 INTROD UCTOR Y.

the discharge of function and for the production of heat, it is oxidised, and, chiefly in the form of carbonic acid and urea, pusses from the system. While the hmgs and the kidneys are distinguished each by the large excretion of a special substance, all three, the lungs, kidneys, and skin, are connected by the removal of a common substance, water ; and their work in relation to this is vicarious. When more water is carried off by one means, less escapes by another. This relation between the skin and kidneys is recognised by every one. In cold weather, when the skin acts less, the kidneys remove more water ; in hot weather, when the skin is active, the kidneys remove less.

But the perspiration is not simply water ; other substances, although only in very small amount, are constantly found in it. The chief of these are inorganic salts, such as sodium chloride, or common salt. But there are also traces of urea and of carbonic acid.

The quantity of perspiration, or the amount of fluid lost by the skin, is deter- xnined by various causes both from within and from without. The influence of exercise on the action of the skin is obvious to every one. Then the external temperature, the amount of moisture already present in the air, and its stillness or motion, affect the amount of fluid that escapes by the skin. Some of the water forthwith evaporates, and disappears as insensible perspiration, and some at times collects on the surface and bedews it, or even runs off in drops. The amount of sensible perspiration is by no means always in proportion to the total amount which is formed, for the external conditions already mentioned largely determine whether the sweat shall disappear as vapour or collect on the surface.

The evaporation of water from the surface is an important means by which the temperature of the body is reduced and regulated. This will be readily understood when the amoimt of heat which must be concerned in converting water into vapour is considered. And hence one important effect of clothing. Man is distinguished from animals by his nakedness — by the absence of all means which lessen the escape of heat from the skin — and his clothing in this respect is an artificial substitute for fur and feathers. It not only checks loss by direct radiation, but it also greatly interferes with evaporation.

The sweat is formed by minute glands, which are everywhere thickly set in the substance of the skin. Some fluid may escape by simple transudation through the skin in the intervals between the glands, but we have no means of determining what proportion this bears to the rest. But besides these glands, called sudoriparous, there are others which especially abound in certain parts. These, which are called sebaceous glands, secrete an imctuous substance, which lubricates the surface, and plays an important part in maintaining the texture and properties of the integu- ment It is this substance upon the surface that causes the difficulty in wetting it thoroughly with water, and that can be removed only by prolonged scrubbing with the use of soap.

Between such substances as carbonic acid and urea on the one hand, and the constituents of certain fluids which are formed from the blood on the other, it will be observed that there is this distinction : the former when separated are forthwith cast out of the body, and are therefore called excretions, while the latter, as in the

GLANDS AND THEIR FUNCTIONS. 19

case of the bile already noticed, are destined to some farther purpose in the economy, and are therefore distinguished as secretions. What may be the ultimate destina- tion of some of these secreted substances, as, for example, of the constituents of the gastric juice and saliva, we do not at present precisely know, but in the instance of the bile, which mainly consists of substances rich in carbon and hydrogen, there is strong evidence to show that these, after playing the part already mentioned in digestion, are re-absorbed, and regaining the blood, are finally oxidised, and by their combustion assist in the production of heat. And with regard to the formation of these various substances which are thus by various organs drawn from the blood, there is this further difference to be noted : that some of them, as carbonic acid and urea, are constantly found in the blood itself, and are only separated from it by the organs through which they are excreted ; whereas others, as certain constituents of the bile, do not exist as such in the blood, but are formed out of it by the action of a special organ.

Organs, such as the liver, pancreas, and kidneys, whose office it is then to separate various substances from the blood, are called glands. They are composed essentially of minute bodies, called cells, which are the active agents in the process. The product of the action of these cells is collected into minute channels, which conduct them into larger ones formed by their coalescence, until at length they flow away from the gland through a single tube, or duct. But there are other organs in the body also, unfortunately called glands, which in structure and function differ greatly from these. ■ The spleen is called a gland, but it has a remarkable structure which does not separate any material from the blood, and therefore needs no duot. The glands in connection with the lacteals and lymphatics have been already mentioned. These, which are small and very numerous in many parts of the body, are in structure and function very nearly allied to the spleen, and the great "tract of mucous membrane — the membrane that lines the great cavities which communicate with the exterior, as, for examples, the digestive canal and the respiratory tubes — this mucous membrane is in some parts very rich in minute structures set in its substance, which have functions similar to those of the lymphatic glands. The spleen and similar structures are sometimes distinguished by the term ductless glands, but they are better known by their function. They are concerned in the development of the blood. The fact has already been noticed that the lymph, after passing through the glands, is much richer in white cells, and the blood, after leaving the spleen, yields evidence of considerable improvement. The physiology of these important structures has not yet been thoroughly worked out, but enough is understood to justify the title by which they are at present generally known — blood-elaborating glands. The great liver itself, in one of its offices, belongs to this class. In the manufacture of bile it is a secreting gland, but the blood itself is greatly altered in its passage through the liver. By the arrangement of the circulation, all the blood that goes to the stomach and intestines finds its way directly afterwards to the liver. Tlie capillaries of the stomach and intestines lead, as usual, into veins, which collect into larger ones that at length form a single vein ; but this, instead of making its way directly to the heart, passes to the liver, through which its blood is distributed, to be again collected into

K) JNTROD UCTOR Y.

Urger veins, which go, with the rest, to the heart. Thus, whatever is absorbed by the blood-vessels from the stomach and intestines — that is, all the substances of the food which have been completely dissolved — are subjected to the action of the liver before they find their way into the general mass of the blood. The blood, then, going to the liver from the stomach and intestines, must be, during digestion, largely charged with crude materials, and when it leaves the liver these have been very considerably elaborated. There can be little doubt that these two great functions of the liver, the elaboration of blood and the formation of bile, are very closely related ; that one action is the complement of the other.

7'A« Animal Functions, or tJie Functions of Helation.—rJje&ying now the functions of organic life, those which are directly concerned in the maintenance of the indi vidual, and turning to organs of another class, the so-called organs of animal life, or those which minister to the function of relation, let us glance first of all at ihi Skeleton. No fact in anatomy is so obvious to all as the contrast between tht bones and the soft parts of the body. The great hardness of the bones, due tc the earthy matter they contain, their passive character to casual observation and their endurance for ages after all other parts have decayed and disappeared suggest to many a very false view of their nature. The bones, like other organs oi the body, are living structures ; like other parts, they are subjected to natural anc morbid changes ; they exhibit similar phenomena of health and disease ; the} suflfer, as other li\'ing structures do, from injury, and are capable, as may be seei any day, of veiy perfect repair ; a broken bone, in favourable circumstances, ii restored to its original condition. In truth, the bones^ which are in the firsi instance formed from cartilage, or membrane, belong to the class of tissues called fibrous; of tissues which are composed of extremely delicate and simph fibres, variously interwoven, such as tendons and ligaments, and that remarkabL tissue which is found all over the body, and is so abundant in many parts, whici binds together difierent organs and the proper structures of the same organ, and ii therefore called connective tissue. The bones, like these structures, are suppliec with blood-vessels and nerves, but, like them, sparingly, in comparison with th( more highly-endowed structure of muscles and nerves. The bones owe their mos obvious characters to the infiltration of their fibrous framework with the salts o lime in the form of minute granules. About one-third of bone consists of anima matter, in the form of fibrous tissue, and two-thirds of mineral matter, compose( chiefly of calcium phosphate and carbonate. When a section is made through th( substance of bone, its texture appears to be very difierent in difierent parts. At th( surface, and for a variable depth inwards, the texture is compact, so dense that t( the naked eye it is smooth and uniform, and can be polished like ivory ; but in thi deeper portion the texture opens out so as to become sponge-like, or cancellous, an( the minute spaces thus formed are very visible to the naked eye. The contrast betweei compact or dense bone and cancellous or spongy bone is usually obvious enough, an< yet it is but a question of density. To the microscope, bone everywhere exhibit the same structure ; the difierence is simply due to closeness of arrangement.

In the shaft of the long bones of the limbs the cancellous tissue rapidly disappear toward the centre, so that there a single cavity is formed, which is filled with a kin(

THE HUMAN SKELETON. 21

of fat, called marrow ; but iii the interstices of the cancellous tissue everywhere, a soft albuminous substance, marrow of another kind, is found. Different bones vary much in hardness and density. In some parts the compact tissue is almost cancel- lous, in others it is almost as hard as ivory. The strength of bone, the arrangement of the compact and cancellous portions, and even the plan or pattern of the cancellous tissue itself, is evidently in relation to the degree of resistance required. This is beautifully shown in a longitudinal section through the head and neck of the thigh- bone. The cancellous tissue is here, for the most part, arranged in the form of tiny Gothic arches, rather regularly superimposed, the columns of each arch resting upon the apices of two subjacent ones, and all having a direction corresponding with the long axis of the neck, that is, in the plane through which the lines of greatest force usually pass.

The great strength of bone, its hardness and power of passive resistance, is its most obvious feature, but it has other qualities that are eminently useful, and must not be overlooked. The texture of bone in some parts, as in the spine in front, and about the neighbourhood of joints, is less brittle, or, as it may be expressed, more tough than elsewhere. But all bones are more or less elastic. This property is very conspicuous in the ribs, out of which bows have been formed. But even a skull, if allowed to fall on a stone-floor, will rebound with considerable force.

The quality of bone varies at different periods of life. In infants, many of the bones, before they are fully infiltrated with earthy matter, will readily bend, and sometimes at this age, when they are broken by being bent, they will crack after the fashion of a green stick, only half through, on the convex side. They are stronger during the middle period of life, and in old age they are more easily fractured. It has been supposed that this is due to their increasing brittleness from the loss of animal matter, but it is, at least in many cases, chiefly due to the loss of substance altogether. In those who grow lean and spare in old age, the bones, like other parts, suffer loss of substance. They become lighter, and this lightness means loss of strength. When the bones alter in composition, it is usually by the increase of fat, which sometimes then pervades their texture, and forms a part of that general fatty degeneration and accumulation to which a class, in the decline of life, are prone.

The skeleton constitutes by weight about one-sixth of the whole body, and con- sists of upwards of two hundred distinct bones. In the first place there is the spinal column, composed of a series of bones very closely and elaborately locked together, and enclosing throughout a canal, in which is lodged the spinal cord. The spinal column gradually increases in size from above downwards. It is not quite straight, but forms a series of alternate curves. In the neck it is very slightly convex forward. In the back it forms a long and rather bold curve- backward. In the loins it is again slightly curved forward, and once more below it is bent backward. Although the movement between any two bones, except the two first, is very slight, the whole column is very flexible. Upon its summit is the skull, containing the brain, which, with the first bone of the spine, is capable of very free movement. To the bones of the spine in the dorsal region are appended, on either side, the twelve ribs, the majority of which, extending round to the breast-bone in front, enclose and protect the cavity of the thorax, which contains the heart and lungs. Upon the upper part of the thorax are

SB INTRODUCTORY.

two bones, fonning the shoulder-girdle, to which are attached the bones of the upper extremity. Below, firmly bound to the bones forming the lower end of the spinal column, which have coalesced into one strong wedge-shaped piece, are the two haunch- boneSy which enclose a cavity called the pelvis. A deep socket on their outer surface receives the head of the thigh-bone. The upper and lower extremities are formed on a similar plan. The arm and thigh have each a single bone. The fore-arm and leg have each two bones. To these, at the wrist and ankle, succeed a number of small bones, and to these the bones of the fingers and toes. Between the chest and the pelvis is a si)ace not surrounded by bones, called the abdomen. This cavity, which contains the organs of digestion, is separated from that of the chest by a partition composed of a powerful muscle and its tendon, the diaphragm. This muscle has been already noticed as the chief agent of inspiration. If the skeleton, therefore, were bisected longitudinally, either half would show the plan upon which the different cavities it contains are arranged. A comparatively small posterior cavity, forming the spinal canal and the cavity of the cranium, and containing the great nerve- centres, would be separated by a bony wall from a large anterior cavity, containing the whole digestive tract from the mouth downward, and the organs of circulation and respiration.

The joints which are formed between the bones admit of being divided into difierent classes. In some, as in those of the skull, the bones are very firmly locked together, and there is no movement between them. In others the movement is extremely limited ; two surfaces, more or less flattened, glide slightly on each other. In this case, although the movement in any one joint is always within a narrow range, yet when several such joints are close together, as in the instance of the wrist and foot, the total amount of motion may be considerable. But in other joints, the actions of which are more familiar to us, the movements are very free. Sometimes the joint is constructed after the manner of a hinge, admitting only of a to-and-fro movement, but through a wide range. The most striking instance of this is at the elbow joint, between the bone of the arm and one of the bones of the fore-arm. This joint permits of flexion, as when the fore-arm is bent on the arm ; and of extension, when it is carried backward and straightened. Then the most complete joint of all, that which admits of the greatest variety of movement, is the ball-and-socket joint, as at the shoulder and the hip. The arm and leg can be carried forward, backward, inward, and outward, can be carried round so that the hand and foot may describe a circle, and, in the case of the arm especially, the limb can be rotated on its own axis. These joints, and that of the thumb, are the most movable in the body. That portion of a bone which enters into the formation of a joint and is called its articular surface, is capped with a layer of cartilage, or gristle, and this presents a smooth and highly-polished surface. The ends of the bones are bound strongly together by ligaments, and more or less supported by muscles, and the surfaces of the bones and ligaments are lined by a delicate membrane which forms a more or less complete sac, or bag, and secretes just enough of a viscid fluid to lubricate the opposed surfaces, so as to enable them to work upon each other with the least possible amount of friction ; hence the popular term for it of joint oil In the instance of certain joints, as those of the

MUSCLES. 23

knee and lower jaw, an additional structure is introduced to prevent still further any miscliief that might arise from any sudden and violent contact of the surfaces. A plate, or layer, of dense tissue, a mixture of fibrous tissue and gristle, shaped in adaptation to the surfaces, is interposed between the bones, where its acts as a buffer. In the case of the spinal column, no actual joints exist between the bodies of the numerous bones which compose it, but between adjacent bones a thick layer of tough and elastic material intervenes. This, although united firmly to the bones above and below, yet allows of some play between them, and the total effect of this arrangement throughout the column is to afford a considerable extent of motion. In the case of joints that are not very movable, the bones which form them admit of being bound together very firmly by strong ligaments ; but when the movement is very free, the ligaments, which are not elastic, must be comparatively lax. In the latter forms additional security is given by the support of powerful muscles.

Besides the more obvious purposes of joints connected with their movements, they play, no doubt, an important part in counteracting, by their construction, the effects of shocks and sudden jars. For instance, if one continuous structure extended from the feet to the head, the effect upon the brain of jumping down from a height would be very different from what it actually is, and no one studying the construction of the spinal column can overlook the purpose which is thus secured. In the foot, again, is another admirable example of the effects of a similar arrangement. Between the ankle, heel, and base of the toes there are a dozen bones, and between some of these there is scarcely any perceptible movement. But, as all know, a well-made foot forms an arch when a person stands upright ; the whole sole of the foot is not in contact with the ground, but only the heel and the base of the toes. On the inside there is a considerable interval under the arch. Now, upon the summit of this arch the great bone of the leg rests ; in other words, upon this point falls the weight of the body. The bones of the foot hereabout are more or less wedge-shaped, so that, after the fashion of a properly-constructed arch, the greater the pressure, the more firmly are they driven together. But beneath, this arch is sustained by very powerful ligaments, and thus in the whole structure there is not only much play, but in transmission the lines of force are broken.

The Muscles, which form flesh, and are recognised as the lean of meat, constitute the great bulk of the solid part of the body ; nearly half of the entire weight is due to muscles. There are two kinds of muscle : one, the most powerful and abundant, forming the large masses of flesh, of a dee]^ red colour, comprises the active agents of the sensible movements of the body, as of the limbs. They are attached to the bones, not directly but through the intervention of tendons. Thus they have two points of attachment, between which they act. The more fixed of these is called the point of origin, and the more movable one the point of insertion. These muscles, upwards of five hundred in number, are, for the most part, under the control of the will, and hence are termed voluntary muscles. Their substance is composed of fibres which, under the microscope, exhibit fine transverse stripes : hence, again, these muscles are sometimes called striped, or striated muscles. They are richly supplied with blood-vessels and nerves ; in short, they are very highly-endowed structures. But besides these there are muscles of another kind, whose characters are not so obvious.

i4 JNTBODUCTORT,

These, whose existence and action has been already alluded to, are found as a oonstituent of the walls of various tubes ; of the gullet, where they form a comparatively thick layer, of the stomach, of the whole of the intestines, of the smiUler aiteries and tlie veins, of gland ducts. They are usually arranged in spiral layers, the external ones more nearly longitudinal, and the internal more nearly circular. They, too, are composed of fibres ; but these differ in size and shape from those of voluntary muscles, and they have no transverse stripes. Hence, these ai-o known as plain, or unstriped muscles ; or, because their action is not under the control of the will, involuntary muscles. Their office, as already mentioned, is, by an action called peristaltic, to propel onward the contents of the tube.

The heart, as previously stated, is a muscle, but of a somewhat peculiar kind. The fibres are striated, but smaller and finer than those of voluntary muscle, and its action is not under the control of the will.

All muscle, of whatever kind — and other forms are to be found in the lower f^nimalft — is distinguished by a remarkable property, which is peculiar to it, and belongs to it only as a living structure. This is contractility, or, as it is sometimes (though more vaguely) termed, irritability. Muscle has, when stimulated, the power of active contraction, of approximating its ends, of becoming shorter, and thus it moves the parts, as the bones, to which it is attached. When a muscle thus acts or contracts, its total bulk is not altered, for what is lost in length is gained in thick- ness, so that, in action, it swells up and becomes firmer. This change will be at once understood if, while the fore-arm is being bent, the front of the arm above its middle is grasped by the other hand. The lump which is felt is the substance of the biceps muscle during its contraction. This peculiar property of contraction, by which a muscle may be shortened about one-thii-d, is a vital one, for it disappears with the life of the muscle. A dead muscle is rather tough and somewhat elastic, but no longer irritable. The power with which a muscle contracts is undoubtedly very great, but it is not easy to measure it precisely. The following illustration may suffice. The great tendon which is inserted into the heel-bone, the so-called Tendo Achillis, is one of the strongest in the whole body, and this strength is owing to its physical properties. When removed from the body, it has sustained a weight of 2,000 lbs., yet sometimes by the sudden action of the muscles of the calf, to which it belongs, it has been snapped across.

Muscles may be excited to action by various means. In the living body they are naturally excited through the nervous system. An impulse is conveyed along a nerve to a muscle, and it forthwith contracts, and the nerve so supplying it is called, on this accoimt, a motor nerve. But a muscle may be excited powerfully to contract by an electric current. When a living muscle is removed from the body, it may be made to contract by various mechanical stimuli, such as pinching or pricking ; but when a portion of a muscle is thus treated, it is observed that the contraction does not involve the whole muscle, but only the part that is stimulated, and perhaps the fibres immediately adjacent to it. Powerful chemical agents and heat will produce like effects. This contractility is a property of the living substance of muscle, and the act of contraction, or the work of the muscle, involves the consumption or oxidi-

THE MUSCULAR SYSTEM. 25

sation of a portion of its tissue. After a muscle has been for some time in action, the products of the necessary chemical changes may be collected. A definite relation exists between the amount of work done and the amount of muscle transformed. Heat, too, is evolved during muscular action. When a muscle contracts, its tem- perature rises a degree or so. During the active contraction of a muscle, sound also is produced, a dull rumbling sound, which has been compared to that of distant carriage-wheels. And, lastly, during contraction changes also occur in the electrical condition of a muscle, but the nature of these changes is not as yet clearly under- stood.

Muscles are not highly sensitive structures in the ordinary acceptation of the term. When the skin is divided, far more pain is felt than when a muscle is cut, yet, nevertheless, the voluntary muscles are in very close and delicate relation with our consciousness. A very fine perception of their exact state and degree of contrac- tion must be a necessary condition of our control and direction. That minute ad- justment of force which we are enabled to apply to any desired end must depend on the existence of what has been called a muscular sense. It is through this, for in- stance, that we are able to appreciate the weight of a body. When we hold anything in the hand, we judge how heavy it is by the degree of force required to sustain it, and our estimation of this must be by a subtle consciousness of muscular efibrt.

It is probable that almost all our voluntary actions involve the contraction of more than a single muscle, oftentimes of very many. And in anatomy, muscles are classified into groups, according to the general direction in which they act. Thus, there is a group of muscles in front of the fore-arm called flexors, which act upon the hand and fingers, and another group behind, their natural antagonists, called ex- tensors. Besides these, in the hand itself, there are nineteen muscles ; in the sole of the foot an equal number. While each of these and every other muscle of the body has some action peculiar to itself, in its ordinary work, it is, no doubt, for the most part, associated with others.

This harmonious combination of groups of muscles in various actions is accom- plished by the nervous system, and in relation to this, it is interesting to note that muscles which are accustomed to act together are often supplied by branches of the same nerve-trunk. Much depends, therefore, in our various movements, not only on our power to direct and control the action of any particular muscle, but also on the power we possess of combining several muscles in their action for any given purpose. This power of co-ordination, as it is called, is very greatly strengthened by practice. Certain movements that involve the combination of several muscles can, at first, be accomplished only with considerable difiiculty, but, by practice, the muscles at length get into the habit of acting together, and by-and-bye it may become almost as difficult to disassociate them.

The great majority of the muscles are attached to levers which are formed by the bones, and in the body there are instances of each kind. The movement forward and backward of the head upon the spine, as in nodding, is an instance of the first kind of lever. The fulcrum between the weight and power is at the articulation ; the weight is the head and face in front, and the power the muscles at the back of the neck. The muscles that depress the lower jaw and open the mouth act on levers of

» INTRODUCTORY.

the second kind. The fulcrum is behind, at the joint, the power is attached in front, and the weight or resistance lies between them. The action of the biceps muscle on the fore-arm is an obvious instance of the third kind of lever. Here the fulcrum ia at the elbow-joint, the weight at the hand, with whatever may be in it, and the power between the two, just in front of the fulcrum.

Muscles frequently act on levers of the third kind ; that is to say, so far as power is concerned, at a mechanical disadvantage, and in some of these instances the power is so near the fulcrum, and the weight is so distant^ that the disadvantage must obviously be very great. But then it should be remembered that what is lost in force is gained in velocity, so that here is no evidence ef wasteful expenditure of sti-ength.

Elastic tissue plays an important part, and an economical one, too, in certain movements, and this simply by means of its physical property of elasticity, which it possesses in perfection. This elastic tissue is, of course, passive until either extended or compressed by some force, and this force is usually muscular action, when, as the force is remitted, it recoils with proportionate power. Thus, its use is commonly considered in relation to muscular action. It may either assist muscular action, be accessory to it, or it may be opposed, acting in the contrary direction. Elastic tissue is usually rendered active by stretching ; sometimes, however, it is compressed. As illustrations of these several modes and purposes of action, may be mentioned the elastic structures connected with the bodies and plates of the bones of the spine, the elastic wall of the arteries, and, above all, the vocal chords.

Fmi/hermore, structures adapted to motion are so provided that movement shall occur with the least possible amount of friction or loss of force. As already stated, the joints are lined with a highly-polished membrane, and provided with an unctuous secretion for this purpose. Tendons of muscles also play in sheaths of similar construction, and so glide smoothly on each other without friction ; and the great organs of the body which are subjected to constant movement, the heart, the lungs, the stomach, intestines, and other abdominal viscera, and even the spinal chord and brain — for the brain has distinct, though slight, movements dependent on its circulation — these chief organs are enabled to glide without friction on the walls of the cavity in which they are contained, by an arrangement similar to that which prevails in the joints. The delicate, highly-polished membrane which invests them, and which is continued without interruption on to the opposite wall, secretes just enough of a watery fluid to keep its surfaces moist. These great serous membranes, as they are called, engage a large share of the attention of the physician and surgeon, on aocount of their liability to disease and especially to various forms of inflammation.

One of the chief characters of man, that by which he is especially distinguished from all animals, is the high degree of development of his Nervous system. This system, which in some form or another may be detected in all animals, save the lowest and simplest, appears at first, of course, in a very rudimentary condition, and it is only by tracing it from below upward, and studying the successive steps of its evolution, that we are enabled, at all adequately, to interpret its physiology in man.

THE NERVOUS SYSTEM, 27

In structure and function two distinct parts may be recognised in the nervous system ; the nerves, which are cords composed of bundles of fibres, and masses of nervous matter called centres, which, in addition to fibres, contain cells with which the fibres are connected. The nerve fibres, which by their aggregation into bundles form the nerves, are comparatively simple structures. They are composed of an almost transparent, semi-fluid substance, contained in a sheath. The so-called nerve-cells, which are sometimes regular and spheroidal in shape, sometimes very irregular, with branching processes, are composed, too, of a stru'^tureless substance, some form of protoplasm. The continuity between the fibres and cells may sometimes, but not always, be distinctly traced, and the so-termed branches of some of the cells are probably the remains, or ends, of the fibres in connection with them which have been broken ofi". Now, the presence of aggregations of these cells, besides the fibres, gives a distinct character to nerve substance which then forms a ganglion, or nerve centre ; so that the nervous system consists of nerves, which are only fibres, and of nerve centres, which always contain, as an essential part, nerve cells. Owing to the presence of these cells among the fibres, nerve centres, or ganglia, may usually be at once distinguished from nerve cords by their shape, and sometimes by the aggregation of several centres into one mass, organs of great size and of still greater importance may be formed. Thus, for the chief examples, the human brain and spinal cord are constructed.

Now let us glance at the constitution of the Nervous system.

In one of the simplest forms in which it appears in some of the lowest animals, it consists of a single ganglion, or centre, with two cords, one extremity of each of which passes into the ganglion, while the other is distributed to different parts.

The first step onward in the progress of the nervous system is that the centres are repeated, and the number of cords proportionally multiplied. The ganglion is no longer solitary, but we find another and then another, until by repetition many appear. The ganglia, as they thus become multiplied, vary in their position ; they are either regularly placed, as in a beetle, or irregularly, as in an oyster. This, their relative arrangement, is of little or no importance to their physiology. It, however, must be remarked that when the centres are thus multiplied they are foimd to be not only connected to cords which are distributed to various parts, but also, by means of other cords, they are connected, in most instances, directly with each other. These latter cords, which are distinct from those of distribution, and establish a direct relation between different ganglia, are called commissures.

The next step in advance, which is almost coincident with the former, is that certain ganglia manifest functions different from those of the rest ; they have peculiar or special offices. The principal of these special ganglia are immediately connected with the organs of special sense.

Lastly, these several ganglia, thus variously distributed, are brought into still closer relation. They coalesce, so that compound ganglia are formed. Thus, a nervous mass, apparently simple, may consist of several really distinct ganglia, which have thus become blended. The plan of this coalescence is beautifully shown in th« metamorphosis of insects. Even here the primary ganglia are still connected only by fibres or commissures, so that, whether ganglia are visibly distinct and

V INTRODUCTORY.

separate, being connected only by long commissures, or whether, coalescing, they are brought into connection by shorter conunissures, is not a difference of such import AS it might at lirst sight appear to be.

Therefore, in man, in whom the nervous system is found to be most highly de- veloped, we trace, in a remarkable manner, tlie result of these several steps of pro- gress. Large, highly -developed nerve-centres — the spinal cord and brain — connected with very numerous cords ; in their nature compound, being formed, as comparative anatomy and their own development sliow, by the coalescence, more or less complete, of many distinct centres. Some of these are endowed with special offices. And with all this evidence of an advanced state of development, the nervous system, in relation to the several functions of the body^ rises to a condition of supreme importance.

The spinal cord, lodged in the spinal canal, forms one long continuous mass, from the sides of which numerous nerves spring in regular succession. Above, it termi- nates in a somewhat expanded portion, called the medulla oblongata. This, and, through it, the spinal cord also, is connected with various ganglia situated at the base of the skull, and these are surmounted by the largest, masses of nerve substance of all, the brain proper, or the cerebral lobes.

It may be mentioned that, in each of these several centres, two kinds of nervous matter may be recognised very easily by their colour, the white and the grey. The white consists for the most part only of fibres, but the grey matter is composed chiefly of cells. In the spinal cord, the grey matter is in the centre surrounded by the white; but in the brain the grey matter is found on the surface, where it is arranged in the foi-m of numerous complex folds, which are called convolutions.

Now the cords, the anatomical elements of which are fibres, and the centres, the anatomical elements of which are cells, differ greatly in their function.

If one end of a living nerve-cord be irritated, an impression of some sort is con- veyed to the opposite extremity. Such an impression is sometimes called a nervous impulse ; but what happens to the cord we do not know. Like telegraph wires, the nerves do not betray by any external sign that news is speeding along them. Like these wires, in order to be fit for service, they must be entire ; and, in some other respects, the transmission of such an impulse is analogous to a current of electricity, and to this it has often been compared ; but it is certainly not altogether identical with it, for it differs from it in some important respects. Some form of molecular disturbance in the nerve-fibre is assumed, and probably upon good grounds. The fact, however, is clear that the function of these fibres is the transmission of impres- sions. The nerve-centres also, and this by virtue of the fibres they contain, can conduct impressions, but they have other and higher offices by which they are distinguished.

When an impression is conveyed by a nerve to a nerve-centre, this may dispose of it in various ways. It may reflect it. Now this reflex action appears to be the chief ; it certainly has been the most fully studied, and is the best understood of the functions of a nerve-centre. By reflex action is meant the power which nerve- centres possess of receiving and perceiving an impression brought to them by a nerve from some part, and, as the result, of transmitting an impression through another

REFLEX ACTION. i20

nerve to some other, it may be distant, part. Thus an impulse conducted by nerves from without inward, reaches a centre, and by that centre, as the result, an impulse is sent through other nerves which conduct it from within outward. So, it is said, an impression or impulse is reflected by a nerve-centre. If, for a familiar instance, the skin be pricked, the part is suddenly withdrawn. An impression is conveyed from the spot injured through a nerve to a nerve-centre, and hence another impres- sion is sent by the centre through another nerve to muscle, which then contracts and moves the part away.

But although in this instance, of course, pain or sensation — or, in other words, the consciousness of the impression — is concerned, neither sensation nor, still less, any idea, is necessary to the performance of a reflex act, and whether or not such states shall accompany it depends on the centre through which the action takes place. There can be no doubt that those reflex actions which are of most general occurrence are accomplished without the intervention of idea or consciousness, and these, the simplest form of reflex action, are conveniently distinguished by the term excito-motor, which is meant to imply that muscular contraction, or some other result, is the effect of a simple excitation of a nerve-centre.

Numerous actions that are continually occurring in our bodies, and in those of the higher animals, afibrd examples of this kind of reflex function. These, from their very nature, being unattended by consciousness or sensation, escape observa- tion. Without entering further into detail, it may be said that the contraction of plain or unstriped muscles generally is thus excited. That powerful and violent reflex acts may occur without idea or consciousness of them is proved in innumerable cases of disease and accident, where, from some injury to a portion of the spinal cord, the communication between some parts of the body and the higher nerve-centres is cut ofl". In these parts, the most lively movements will often occur, and these are not only beyond the unfortunate person's control, but continue without the least consciousness, unattended by the slightest sensation. That any given movement is adapted to a particular end is no proof that it is not the result of simple excito- motor action. It must not be assumed that the obvious adaptation of a movement to a definite purpose is in itself evidence of the operation of will or the intervention of consciousness ; for a passing consideration of some of our own functions will at once suffice to refute such an idea. For example, what movements are more obviously adapted to a definite purpose than those of the muscles of respiration ? yet we know that neither the will nor even consciousness is necessarily concerned in them, for they work efficiently during the prof oundest sleep.

But next there are actions of a reflex character which produce sensation, involve consciousness, but which are nevertheless involuntary, not only occurring independently of the will, but often in direct opposition to it. Of these actions, which are conveniently termed sensori-motor, there are in ourselves some striking examples. An excellent illustration may be witnessed in the movements and laughter excited by tickling. Here very unequivocal sensations are produced. We are fully conscious of the impressions, and we struggle and laugh involuntarily, even in spite of the will. Coughing, again, is usually another act of the same kind, and many more might be mentioned.

so INTRODUCTORY.

Now, a question comes in hero that is too interesting to be put aside in silence. Why are certain acts thus attended by sensation 1 Why, unlike the former ones, do they involve consciousness 1 More than one beneficent purpose is thus attained.

Dfuiger is thei-cby avoided. For example : if some irritating gas or vapour be drawn into the commencement of the air passages, we at once, by the sensation it produces, recognise its presence, become conscious of the evil, and forthwith adopt means to get rid of it The very unpleasant subsequent effects of the injudicious application of irritant substances to the nostrils during faintness or insensibility is just a hint of what might otherwise occur. Hence an all- wise design of pain, by which we are warned of the advent of mischief, of the stealt^hy progress of disease in time eithei* to adopt measures to avert it or to prepare to meet its consequences.

Again, through sensation and consciousness our daily and hourly acts are sources of pleasure ; acts, be it observed, which are necessary to life and health. Thus, when food is required we become sensible of the want, and its proper supply affords enjoyment.

But hunger and thirst, although distinctly sensations, are yet in a measure peculiar. They are produced through particular nerves, and more or less localised to the region of the stomach and throat, and are suggestive of particular ideas. There are other and still further modifications of common sensation. The sense of touch is closely akin to it, yet not identical, for in the skin, over the whole area of wliich the sense of touch plainly exists, there is by no means in every part a direct relation between ordinary sensibility and the sense of touch. The sense of touch is especially acute, for instance, about the tips of the fingers, but other parts of the surface, as the eyelids, are more sensitive to pain. Moreover, anatomy discovers in the substance of the skin certain conical structures, called papillae, connected with the extremities of nerves whose function is clearly the sense of touch. But it should be observed that the evidence derived from handling various bodies is not solely due to the sense of touch. It is usually assisted by movement and by pressure : in other words, by sensations derived from muscular actions.

In taste sensation is still more highly specialised, but between taste and touch no abrupt line of demarcation appears. The papillae of the tongue are formed after the fashion of the papillae of the skin ; they are more highly-developed structures of the same kind, and the tip of the tongue is the most delicate instrument of touch of the whole body. The sense of smell is closely allied to that of taste, but differs from it inasmuch as while the nerves of taste are conductors of ordinary sensation, the special nerve of smell, like those of sight and sound, conveys only an impression of a peculiar kind. The reflex act of sneezing, however, is provoked through nerves of common sensation. Then, finally, there are those forms of sensation which are emphatically called special ; the special senses of sight and hearing. In either case there are special nerve structures, the essential part of an elaborate apparatus, which receive impressions, and these are conveyed by certain nerves to special centres, where such impressions are recognised in the one case as light and in the other as sound.

Lastly, there are impressions which not only produce sensation and consciousness, but wliich go still further, and excite ideas, and, as the result of these, certain acts

NERVE CENTRES. ' 31

are performed, for the most part, in obedience to the will. These voluntaiy acts that involve ideas have been conveniently termed, in contradistinction to the others, ideo-motor actions.

All these terms, it will be observed, assume motion to be the outcome of the reflex act, and in truth this is usually the most obvious one. Yet the result need not always be expressed in muscular movement. For instance, when food is introduced into the mouth, saliva flows. This is the result of reflex action. An impression is made by food on the nerves of the tongue and other parts ; this is conveyed by them to certain centres, which reflect it, through other nerves, to the salivary glands, and so they are stimulated to secrete. It will be seen that reflex action in any of its forms involves the transference of impressions by nerves in opposite directions. An impulse is, first of all, conveyed by one nerve from without inward, centripetally, and then an impulse is conveyed by another nerve from within outward, centrifugally. Hence, the nerves themselves are usually divided into sensitive and motor ones. But these terms are objectionable in more than one way. In the first place, as we have seen, sensation need not always be concerned, and the result of the act may not be motion, at least in the ordinary sense. But no other terms hitherto suggested are wholly free from objection, and these may, for the present, be usefully retained.

The next question is. Through which centres are these several kinds of reflex actions accomplished 1

The spinal cord and the medulla oblongata, which, as already stated, is a continuation of the cord, and corresponds to the rest of it in the character of its functions, is the centre of the simplest form of reflex action — excito-motor.

For, if the communication between the cord and the centres above it be interrupted so that any impressions which reach the cord can be no longer conducted through it to them, then they are not felt. The person is now not conscious of them. But, still acting on the cord below as a centre, powerful reflex movements may be produced, that are therefore simply excito-motor.

The surpassing importance of the medulla oblongata as a nerve centre is due to the fact that it contains the ganglia, which are connected with the acts of respiration and deglutition ; upon the integrity of these centres the vital function of respiration depends. The medulla oblongata, like the rest of the cord, is always more or less active. Its complete and prolonged repose would obviously be incompatible with life.

There can be no doubt that it is the office of certain centres above the spinal cord and medulla oblongata to produce sensations, and to them impressions must be conveyed in order that they may be felt or perceived by the mind ; and it has been rendered highly probable that certain centres which lie at the base of the brain proper — that is, betweeen the medulla oblongata and the cerebral lobes — and with some of which the nerves of special sense are connected, as those of sight hearing, smell, and taste, are the centres of sensations of various kinds, and of sensori-motor actions, constituting collectively what may be called the sensorium.

Acts which are properly called instinctive are essentially of this nature. The purely instinctive acts cannot be said to be the result of reason. There is no evi-

53 INTRODUCTORY,

dence in them of the necessary intervention of ideas. It cannot, for example, be contended that, on the part of an insect in some of its most wonderful acts — say, of a bee in the construction of its cell, or of an ant in the storinr^ of its food — there is an intentional adaptation of means to ends, founded on definite ideas of the nature of both ; m other words, a calculation of consequences. But this tempting subject cannot be further discussed here.

When impressions are conveyed beyond the centres just alluded to, still farther upward, to the cerebral lobes or hemispheres, results of another order are produced. Ideas arise, and hence the various intellectual functions and consequent acts, which have tlierefore been termed ideo-motor, or, because of the will, voluntary.

It may be mentioned here that there is good reason to believe that impressions from without can only act on the cerebral hemispheres through the intervention of tlie sensorium, wliilst, in like manner, acts resulting from the exercise of the will can only be effected through the sensorial centres to which an impulse is sent from the hemispheres above.

Underneath the back part of the brain proper there is a considerable mass of nerve-substance, called the cerebellum, or little brain. Of this, it must suffice to say that weight of evidence inclines to show that the greater portion of it is engaged in the co-ordination of muscular movements..

It is well known that if an impression be made upon a sensitive nerve in its course, the sensorium, perceiving that impression, refers it, not to the part of the nerve which is excited, but rather to its periphery, to the part to which those fibres that have been impressed are distributed. A familiar illustration of this is presented in the case of the ulnar nerve, at the elbow. When this nerve, popularly called the " funny bone," is there struck, pain is felt, not so much at the elbow as in the last two fingers, the parts to which the fibres are principally distributed. And so, again, is to be explained the well-known fact, that for years after a limb has been amputated, the person will be conscious of sensations in the hand or foot which was removed, when from any cause the nerves in the stump are excited. Now this applies to an impression made upon any part of a nerve, even to its termination in a nerve-centre. If the central extremity of a nerve be impressed, still the impres- sion is referred by the conscious mind to the distal extremity — to its periphery.

This fact affords a key to the interpretation of what are called subjective sensa- tions. If the central extremity of a nerve be excited, the impression is referred to the periphery, and we naturally believe that the part to which the sensation is refen-ed must be the one which is impressed. Thus, if a ray of light fall upon the retina, the periphery of the optic nervCj it is forthwith conducted to the optic ganglia in the sensorium, and there recognised. But if the central extremity of the optic nerve in the sensorium be excited, the conscious mind still refers the impression to the peri- phery— which impression, by the way, is always that of light; for any impression, of whatever nature, made upon the optic nerve is perceived only as light, no nerve-fibre seeming to possess the i)roperty of transmitting or evoking more than one kind of impression. This is, therefore, what is called a subjective sensation. An impression is made within, and the same effect is produced on the sensorium as if the impres- sion had come from without. The sensorium itself cannot draw the distinction. It

FUNCTIONS OF NEBVE-CENTBES. Z6

must be effected by the mind reasoning by the aid of collateral circumstances. Thus, the vision of the dagger was a subjective sensation in the troubled brain of Macbeth — " a dagger of the mind."

It has been already mentioned, in reference to the function of the spinal cord, that a nerve-centre may conduct impressions like a ner've, and, either with or with- out itself dealing with them as a centre, may transmit them to other centres beyond. Out of this fact, in connection with the preceding one, some curious conditions arise. Suppose some nerve be excited, the impression will be conducted to a centre, and from this centre or portion of a centre at which it first arrives, it ma}- be transferred to some other centre or portion of a centre^ where the central extremities of other nerves, which are distributed to other parts, terminate, and these being thus 'excited, the impression is referred by the conscious mind, according to the law just mentioned, to their perij^hery, to the part to which they are distributed, and thus an impression arising in one part of the body may be referred in this way to another part. This is. the explanatioi; of the circumstance with which surgeons are familiar ; that, at .the commencement of disease of the hip-joint, pain is oftentimes felt by the patient in the knee. So, in the same way, disease in one tooth may provoke pain in another, and it has sometimes led to the impleasant mistake of extracting the wrong tooth.

Again, it appears that some nerve-centres can exercise a restraining influence over others, holding, as it were, their action in check. The brain, for instance, seems able, in certain cases, to exert this inhibitory influence, as it has been called, over the reflex action of the spinal cord.

And closely allied to this power is probably that through which numerous im- pressions of various kinds that reach the centres produce no sensible result.

One further question of great importance must be asked in reference to the func- tions of these nerve-centres. In what has hitherto been said of them, they have been described as acting in response to some impulse received or impression conveyed to them from without. Can they act independently of this 1 At first sight it would appear to be very easy to answer in the affirmative, but the question is beset with difficulty. In cei-tain cases, the spinal cord would seem to excite the contraction of muscles as an original act, but there is strong evidence to suggest the fallacy of such observations, and much to show that its natural mode of action is reflex. For the medulla oblongata, again, — which, as already mentioned, contains the centre of respi- ration,— there is some evidence in support of the view that, independently of any impression from the lungs, it can originate impulses which j^rovoke the respiratory act. And at present this is current doctrine. So, again, the general belief is in favour of this so-called automatic action of the higher nerve-centres. Certainly, as we go higher, the evidence accumulates in favour of independent action ; at all events, of action independent of any immediately preceding impulse from without. But then the question comes in with especial force here — How far are these higher centres capable of storing impressions they receive, and of using them in the dis- charge of function, after an interval more or less prolonged ? Such a suggestion is not altogether opposed to evidence. The simplest form of reflex act consumes more time than does mere conduction, and many of the higher or more complex forms of reflex action involve a more elaborate circuit than the lower. It needs hardly to b» 3

84 INTROD UCTOR Y.

added that in the brain itself, and in the operations of the mind, this and almost all difficulties that beset the investigation reach theii* climax ; and it is here especially far more easy to urge valid objections to any view set foi-th than to advance a step oil firm and secure ground.

One fact, however, yet unnoticed, seems tolerably clear. These great nerve- centres are symmetrical. By a longitudinal section they may be divided into two equal and similar portions. But farther than this ; the facts of comparative anatomy, and their own plan of development, go to show that each really consists of two portions, or of a right and left ganglion, which subsequently become more or less blended together. Even in the spinal cord evidence >of tliis arrangement still persists in the form of two grooves, or fissures, in the mesial line, one in front and another behind. These nearly meet, so that the halves of the cord are connected together only by a thin strip of nerve-substance. Higher up, the two portions become still more distinct, and the grey masses on either side are connected only by bands of white fibres. In the brain, the cerebral lobes, or hemispheres, as they are often called, are quite distinct, and their opposed surfaces are not even in contact, and at their base only they are connected by a layer of white fibres. Thus, the brain is double, although the mind is single, and if it be assumed, as it generally is upon strong grounds, that the functions of the two halves for the most part correspond, then it must follow that they work in perfect harmony. As, for instance, with the sense of sight, although we have two eyes, we see objects singly ; so with tliought, although we have really two brains, there is during health no «ign of discord or confusion. This harmonious action is referred to the bands which unite the lateral masses of ganglia, and which are therefore called commissures.

The brain and spinal cord, with the numerous nerves that enter into or issue from them, constitute what is called the cerebro-spinal system, because there is another much smaller system, called the sympathetic, which, however, communi- cates freely with the first The sympathetic system consists of a series of small centres, or ganglia, situate on either side in front of the spinal column, varying in size and shape between an oat and an almond, from which spring very fine and delicate nerves, whose principal destination is the muscular tissue of the smaller arteries, the contraction of which they control, and thus regulate their calibre. Hence, these are termed vaso-motor nerves.

So, then, speaking of the brain and spinal cord, it appears that the spinal cord is not merely a conductor, or channel, through which impressions from without pass to the higher nerve-centres, and from within from the higher nerve-centres to various parts of the body, but that it is itself the centre of that form of reflex action which is called excito-motor ; and that the brain, commonly so called, which includes not only the cerebral lobes but other centres beneath them, that the brain is the organ of consciousness and intelligence, of the emotions and passions, of ideas, of the intellectual faculties — in a word, of the mind.

Yet, with many, there is still a strong — if not strange — repugnance to the idmission that mind holds the same relation to brain as function holds to structure elsewhere. Many shrink from the conclusion as if it involved something dangerous or improper. Why ? Perhaps chiefly because of the confusion which exists in the

MIND AND SOUL. 35

conception of mind and soul, a confusion wJbich lias always prevailed, even to such an extent that by the best known authors the terms mind and soul appear to be employed indifferently. *

And hence it has arisen that when the mind is spoken of, the soul, or spirit, is assumed to be included, and then the terrible charge of materialism is hurled at those who regard the mind as a function of the brain ; nay, so deeply rooted and widely spread is the confusion, that even when the distinction has been drawn it has not been recognised, and passion and prejudice have too often usurped the place of evidence and reason.

A question of this nature, however, is not to be settled by intuition or feeling or rhetoric, or by any appeal to the imagination or desires. Like every other of the kind, if it be a legitimate subject of enquiry at all, it must be determined by evidence. It is not what we think it ought to be, but what we can discover it to be.

This jealousy of research and haste to denounce evidence, not on its merits but because of its assumed tendencies, surely suggests but a feeble faith in the truths which are supposed to be assailed. We say assumed tendency, for what evil of any kind lies in it beyond the disturbance of preconceived ideas ? Is the conception of life really ennobled by the hypothesis of a vital principle 1 Can any evidence of the origin of man touch the question of his destiny % Is the mind less a fact or a force ; are its powers lessened ; or, if you will, is its supremacy challenged if it is demonstrated to be the function of the brain 1 If the mind, or the intellectual part of man, is distinguished from the soul, or the spiritual part, the objection urged in the term materialism loses all its force.

But it has been said that the soul and the mind are not distinct. Yet, howevei difficult or impossible it may be to define them, to understand either, or to disentangle the one from the other in their operations, still in their essential nature they cannot be the same. It is not always easy to avoid the confusion, or to study them apart, because they habitually work together and mutually influence and react on each other. But union is not identity, and their combination in one being does not prove that they are even allied. At all events, in common intercourse, the

* Thus, in one of his essays, Addison says —

"I consider the human soul without education like marble in the quarry, which shows none of its inherent beauties till the skill of the polisher fetches out the colours, makes the surface shine, and discovers every ornamental cloud, spot and vein that runs through the body of it. Education, after the same manner, when it works upon a noble mind,'' &c.

Again, Burke writes —

" On a review of all that has been said of the effects as well as the causes of both, it will appear that the sublime and beautiful are built on principles very different, and that then- affections are as different : the great has terror for its basis, which, when it is modified, causes that emotion in the viind which I have called astonishment : the beautiful is founded on mere positive pleasure, and excites in the soul that feeling which is called love."

" Eloquence the soul, song charms the sense," — Milton.

See also the quotations under the words mind and soul in Johnson's Dictionary. But his description is singularly clear and accurate —

" Mind. — The intelligent power."

" Soul. — The immaterial and immortal spirit of man."

The confusion between mind and soul is stiU further increased by the word spirit, which besides, in other senses, has been and is employed by writers of authority, sometimes for the mind, ol intellectual being, and sometimes for the soul. — See, e.g., Latham's Dictionary — Spirit.

86 INTRODUCTORY.

distinction is practically assumed. For example, we distinguish between the moral and intellectual qualities of a man ; between a clever and a good, or a stupid and a wickcnl man. Thus, in a vague soi-t of way, the difference is accepted, and how far it may be practicable to define it more sharply and accurately need not be ci>n8idered here. But that it cannot be defined is no proof whatever that it does not exist. No one contends that mind and body are the same, yet liow often, even here, in attempting the analysis, do we pass into confusion ? How difficult, nay, impracticable, is it, in many instances, to distinguish the operation of one from the otlier, even here where the problem offers conditions far more favourable to success % No wonder, then, that the spiritual should be confounded with the intellectual part of man. Yet, although they work and are, so to say, blended together, the phenomena they present to us can be explained only by the fact that they are not one and the same. Do the moral and intellectual qualities of a man go together 1 On the contrary, do we not often observe in the same individual an almost complete absence of one, and the highest degree of development of the other? How can this- be accounted for, except on the assumption that they are, in their nature, different I

Again, in what are strictly qualities of mind, men and animals differ, not in kind, hut in degree. There are the same faculties, although most variously developed. There is, at least in the case of the higher animals, the same combination of instinct and reason, although in relative proportion, in some instances, reversed. But only in man is superadded the moral sense, that which brings him into relation with things which transcend his senses ; which are above and beyond them.

Therefore, insisting on this distinction, and regarding the soul or spirit as out of the reach of this enquiry, and speaking of the mind as the sum of the intellectual faculties (for, to avoid still further confusion, the passions and emotions are here left out of consideration), using the word mind in a strict and limited sense, then there are no grounds whatever for assuming the mind to be a principle, or whatever else it may be called, merely resident in or connected with structure in any special or peculiar way, any more than there are valid grounds for belief in the existence of the once-celebrated vital principle ; but there appears to be no other conclusion left to rational inquiry than to regard mind as the function of the brain, or, if the ex- pression be preferred, the brain as the instrument or organ of the mind.

For all we know tends to assure us that mind holds the same relation to brain that function holds to structure elsewhere. Evidence similar to that by which the relation of function to structure in other instances is shown, exists to show that the same relation exists between mind and brain, while there is no valid evidence what- ever to suggest that the relationship in this case is of a different nature.

Here, just as elsewhere, function depends on structure. There is no sign of func- tion apart from or independent of stnicture. Whoever witnessed or expects to witness any manifestation of mind in the absence of brain ? Exercise of function involves change of structure. Just as the movements of the body involve waste and the repair of muscle, so do the operations of the mind involve waste and repair of brain. In either case the products of waste can be collected, and the sources of repair are known. With improvement or impairment of structure, there is corresponding im- provement or impairment of function.

THE BRAIN. 37

No organ of tlie body illustrates so strikingly as the brain the subtlety of this dependence of function on structure. Here, for the most perfect performance of function, there must be the most perfect health of structure. No organ, for instance, so rapidly or obviously as the brain reveals by disturbance of function any mischief in the blood which supplies it. Of all organs, this is oftentimes the most delicate test of any impurity of the blood. Witness the effect of alcohol, or of any excess of carbonic acid, or the delirium of fever.

Here, as elsewhere, the same effects are produced by exercise and rest. What organ, by its function, speaks more plainly of fatigue from excessive exertion ? What organ, when overworked, asserts more imperatively its claim to rest ? What organ, through its function, yields such satisfactory evidence of improvement by healthy exercise, of increase of power by due and proper use, or of degeneration and decay as the penalty of idleness.

The existence of the cerebral lobes is essential to the manifestation of volition " and intelligence. When these are removed, an animal, upon the application of appro- priate stimuli, will still execute various movements to a definite purpose, for the machinery of all the necessary and usual bodily movements is still present, but an external stimulus is now needed to evoke them. The power of originating or con- trolling action, of calling the machinery into play or of checking it, is wanting. By the removal of the cerebral lobes, will and intellect are abolished, but otherwise, no loss of function or faculty can be discerned, for the senses, such as sight and hearing, and all those acts that are called excito-motor and sensori-motor and co-ordination of movement, are preserved. Such experiments, then, point clearly to the conclusion that the functions of the cerebrum are eminently psychical in their nature. It must be added that, in our opinion, these conclusions have not been overturned by the results of more recent experiments, the deductions from which are themselves open to very grave objection.

The results of cerebral pathology are more conflicting and less trustworthy than even those of experiment. As Froude has said of History : " It will provide you <vith abundant illustrations of anything which you wish to believe." Still, it may be fairly afiirmed that, on the whole, the results of clinical and pathological observation afford considerable support to the current view of the function of the cerebral lobes.

The facts of comparative anatomy afford the firmest support to the conclusion that the cerebral lobes are the organ or instrument of the intellectual powers and the will — in shorty of the mind. A comparison of the structure and degree of develop- ment of the brain with the intelligence or mental endowment of different members of the animal kingdom establishes the fact. No doubt the inquiry is open to numerous sources of error, presents many difficulties, has been hitherto very imperfect. And this especially from our want of information of the degree to which intellectual power is developed in any given animal; from confusion and uncertainty of our knowledge on the fact of its manifestation. Witness, for example, what is still often said and written concerning instinct and reason. Still, with all this, and making full allowance for it, there is ample justification for the assertion that, throughout the wide survey which has been taken, a very constant relation has been observed

8d INTRODUCTORY.

between the development of the cerebrum and general intelligence ; that, with in- creasing complexity of the higher nerve-centres, there is increasing variety of the intellectual jwwers ; and that this relation between development of structure and mental endowment may still be traced through the several varieties of man — a truth which |>erhap8 finds rather strong expression in the popular periphrasis of a fool as a fellow " without brains."

As would, therefoi-e, be expected, the brain of man is remarkably large. Although many animals are much larger than man, the weight of the human brain is found to be al>solutely heavier than the brain of any of the lower animals, except the elephant and whale. In relation to the body, the preponderance of the human brain is still more strikingly marked. But, in speaking of the brain in this comparison, it must be borne in mind that the whole encephalon is referred to : not only the cerebral lobes, but the entire contents of the cranium. This, therefore, fails to mark the point to be insisted on with sufficient emphasis. The brain of man — the whole encephalon — is not only remarkable for its absolute and relative size, but also for the far greater development of the cerebral lobes in proportion to the inferior ganglia within the skull. The encephala of other animals owe a much larger proportion of their weight to the other ganglia, and so it comes to pass that in some of the smallest animals the encephala are relatively heavier than in man. In man especially the cerebral lobes tower far above the rest. If, therefore, we compare the cerebral lobes only, excluding the rest of the encephalon, the superiority of the human brain as the organ of the mind is more precisely and far more strongly marked.

Vital Sympathy. — Life, then, in such a complex body as that of man involves the performance of many distinct and various functions by different structures, or organs. But in order that these functions, by which life is here represented, may minister, as they do, to one common end, they all must work in harmony. Therefore, a communication or relation between the several structures and organs must be established, so that the state of any one may influence the rest ; so that while each has a special function of its own, its operation may, within wide limits, be made subservient to other functions which are associated with it. This capability of mutual adjustment, this correlation or co-ordination of parts, is well expressed by the term sympathy. It may be said of all animals which consist of separate parts or of individual structures or organs, that there is, as a necessary condition of their welfare, a sympathy between the parts, or organs, which compose them. And, furthermore, it may be observed that as the complexity of the whole body increases, as the diversity of parts becomes greater — that is, as the grade of development becomes higher — or as the several functions become appropriated each to a special organ, so, as the necessary result, does this sympathy or mutual dependence become more thorough, more intimate and intense. In man, therefore, this sympathy is carried to the extreme, and in him it is difficult to select illustra- tions of it, only because they are so manifold. Witness only the sympathy between the skin and lungs, between the brain, heart, and stomach, or between the eyes.

Now, by what means is this sympathy established? That it is through the nervous system is one of the most familiar facts in physiology. This establishment

VITAL SYMPATHY. 3il

of harmony between divers parts and their functions is the largest, the universal office of the nervous system, and it depends on those properties which have been already pointed out. In the lowest and simplest forms of life in which a nervous system can be demonstrated this appears to be its only function ; at all events, it is the only one that can be at present clearly made out. As the special arises out of the general, and particular portions of the nervous system become endowed with particular functions, this internuncial office, as it has been well termed, is still the most general one ; until even in the highest forms of life, in man himself, where special nerve-centres attain a position of supreme importance, this, the earliest and ever the widest of the functions, still prevails.

No one needs to be reminded of illustrations of the effects produced on distant parts through the nervous system. During health, when all is well, it is less patent to ordinary observation, but in the disturbance of disease it is often made distressingly obvious. To refer to a previous example. Remember what often occurs in a case of continued toothache. The pain, at first limited to the diseased tooth, at length spreads to adjacent ones, then to the jaws, until the original source of the irritation can hardly be distinguished, and by-and-bye it radiates over the whole side of the face and head. The influence, again, of various states of the mind upon the bodily functions is thus transmitted. Thus, shame or anger reddens the face ; thus, fear blanches the cheek and bedews the surface with perspiration.

But impressive as the evidence is of this mutual dependence of parts through the nervous system, it is nevertheless clear that this is not the sole agent of sympathy j there is another even more universal, and perhaps more subtle, if in health still more obscure in its operation — the blood.

The blood is a fluid of most complex composition. Necessarily so, for it is brought into direct relation with food and air on the one hand, and with all the different tissues of the body on the other, in the various processes of digestion, respiration, nutrition, secretion, and excretion. Therefore, it must contain all the substances which the several parts require, receiving these from food and air, and it must receive back worn-out or used-up matters. Wonderful is it, that notwithstanding its complexity and the sources of disturbance to which it is exposed by the continual introduction of raw material on the one hand and of refuse matter on the other, it can and does maintain the uniformity which is necessary to health. Circulating through the body at any given time, we may say, broadly speaking, there is blood in three stages : blood fit for present use, as it were of to-day ; blood which has passed this stage, of yesterday ; blood for future use, of to-morrow. So we can understand that a right state of the blood and healthy nutrition are mutually dependent. The blood must be right for nutrition to be normal ; nutrition must be normal for the blood to be right.

The blood, then, is thus the medium of communication between all parts, by virtue of the incessant changes which go on everywhere between it and the tissues in nutrition. And it is not hard to understand that if any part fails to withdraw from the blood its own proper materials, or restores to the blood substances other than those which are the normal result of the changes it undergoes, the blood must be thereby in some measure, and for some time, affected ; and hence, as a secondary

40 INTRODUCTORY.

result, the nutrition of other and perhaps remote parts, or organs, may in various degraes, through this altered blood, become modified or disturbed. It would perhaps be difficult to over-estimate the part thus played by the blood as the outcome of its great office.

Thus, then, distinct and distant organs may sympathise with each other, or the whole body may sympathise with the condition of any part. In fact, it follows that no single organ in its operation can be altogether independent of the rest ; no changes can occur in i* without influence elsewhere. So the growth, development, wasting, or degeneration of one will determine within limits the condition of another.

Furthermore, by this means we are enabled to explain the effect of severe local injury or disease upon the general health ; for the whole body, either through the blood or nervous system, or both, will soon sympathise with the suffering of any part, and hence that form of fever which is called constitutional disturbance.

The Distinctive Features of Life. — From such a general survey let us now for a few moments attempt to distinguish the essential, fundamental, or primary features of life : those which are universally exhibited whenever life appears, from those which are accessory to these, or associated with them for special purposes in various ways.

And life, even when presented in its simplest form, may be recognised as the crowning distinction between the great kingdoms of nature ; for the difference is infinitely greater between living and dead organic matter than between dead organic and inorganic substances.

And in order to appreciate this distinction, there is no need to exhibit one's ignorance in any attempt to define life, or even to discuss its nature. We are, indeed, baffled in the study of life, as we are by those subtler traits of structure with which vital phenomena are* associated, yet still we may understand and appreciate its effects.

For our present purpose, then, let us consider life as a state of dynamical equilibrium : as consisting fundamentally and universally in a definite relation between destruction and renewal, in a regulated adjustment between waste and repair, .whereby the condition is maintained notwithstanding constant change.

It will be observed that this is no pretence towards a definition of life. It is only an attempt to distinguish life by its essential features, when reduced to its simplest terms and divested of those elaborate details which belong to it in its more complex forms, from those changes and their effects which are more or less visible in all inanimate bodies.

Life is not a state of resistance. Very erroneous views prevail on this point. To say the least, changes are as active during life as after death. The proofs of this are conclusive and clear. "We have only to remember that a living person, in ordinary circumstances, in the course of a year consumes, roughly speaking, something like 800 lbs. of solid food, about an equal weight of oxygen, and perhaps 1,500 lbs. of fluid ; that, notwithstanding this vast supply, amounting in the aggregate to more than 3,000 lbs., his condition during the greater portion of his life remains the same, or nearly so, inasmuch as all this matter, after being wrought into his struc-

DISTINCTIVE FEATURES OF LIFE. 41

ture and forming a part of him, is cast off in quantity exactly equal to that taken in, but widely different in the forms which it assumes, that is, in the manner in which the several elements of it are arranged.

Change and destruction is an inevitable condition of the manifestation of life. It is involved in every act. So the power of compensating this, the repair or reproduc- tion necessary to maintenance involves that of assimilation, which is the power of converting foreign substances into the structure of the body : in other words, the power of appropriating food.

Any adequate conception of life must include both these conditions, destructioii and renewal, consumption and supply. For instance, life is not a state of change only, as opposed to stability, for this is everywhere simply a question of degree, de- pendent on the conditions to which bodies are exposed. Neither dead organic nor inorganic bodies are imrnune from change. Again, life is not peculiar as a process of repair only, for it is well known that this may occur in inorganic bodies. If, for example, portions of crystals be broken off, and if the crystals thus damaged be placed, under favourable circumstances, in appropriate solutions, they will be repaired. They will not at first uniformly increase, but the edges or angles or portions of the surface which have been chipped off will be restored, so that they will perfectly recover their original geometrical form. This, therefore, is repair or reproduction apart from life.

But in life there is the constant and concurrent operation of these two pro- cesses. Both actions are involved in the idea of life, whereby it is distinguished from mere change on the one hand, and from repair on the other. Thus, while in- organic and dead organic matters tend toward a state of statical equilibrium, during life the equilibrium is the result of compensating actions. It is djmamical.

Change, ceaseless change, then, is the necessary condition of life. The idea of temporary unchangeableness is altogether an illusion. We are never quite the same, even for a moment. That life is a flame, that it is a vapour that vanisheth away, are images no less true than trite. A living body, an organism, is a form through which vast quantities of matter are rapidly passing. The human body of an average weight — say of 140 lbs. — is a form through which at least more than a ton of material passes in a year.

Let this prime fact be thoroughly understood. All this vast amount of material does not merely come into contact with the body, and then pass off; but each par- ticle, in its turn, enters into the composition of the body itself, replacing others that have gone before, to be itself replaced by others that are to come. The body is not merely a vessel in which matters are burnt, it is itself the very fuel which is being rapidly consumed.

Change, disintegration, destruction, is inevitably associated with the discharge of function. Every, even the slightest, action, every movement of a finger, every glance of the eye, nay, every sensation, every thought that flashes through the mind, •costs structure, uses it, involves its consumption as a necessary condition.

It is a fact which is too often overlooked, that the changes which occur in any structure are always proportional to the activity of its function. The more an organ is used the more it wears, or rather wastes, away.

Some, perhaps, may be disposed to think that more modern researches have shaken

42 INTRODUCTORY.

the old ideas of the relation in which structure stands to function. These experi- ments and calculations may perhaps at first sight seem opposed to the view which has been so long and universally entertained of the relation of structure to function, that the exercise of function involves the consumption of an equivalent amount of structure ; for these go to show that the work done by muscles, for instance, cannot be accounted for by the amount of their tissue which is consumed in the act ; that the weight of their tissue which is transformed, as calculated by the measurements of the chief products of their decomposition, would not explain the amount of their actual energy. Still, it may be remarked in passing that in the present state of our knowledge the alternative is not inevitable, that the excess of force comes directly or simply from the transformation of food, or that certain constituents of the food, by their oxidation, yield force to the muscles, without necessarily passing through the form of muscular tissue ; thus regarding a muscle " simply as a machine for getting work out of the oxidation of non-nitrogenous food."

But even if this were established, that motor force may be developed, like heat, by the metamorphosis of constituents of the food which are not converted into living tissue ; that structures may transform force derived from other substances without the expenditure of an equivalent amount of their own material ; still, it would not affect, from our present point of view, the relation in which structure stands to func- tion. Still, for instance, the muscle would be the necessary material or instrument by which force is transformed or set free; still the exercise of function woulcj involve the consumption of structure.

If it be asked why the eflfects of such constant and rapid consumption are not more obvious, how it is that the man or woman appears in the same person month after month, or year after year, scarcely, if at all, to our perception, changed, the answer is simply, because in life the demand and supply, w^aste and repair, are ex- quisitely adjusted. The illusion of temporary stability depends on the fact that, in health, perfect and complete renewal waits upon destruction. This is, in a word, nutrition. In life, the various structures are maintained in spite of wear and tear, and, therefore, the constant loss is not apparent. When, as after death, decay alone proceeds, the body disappears.

In certain structures, however, the very limited period of existence which is a condition of every part is obvious enough. For instance, every one knows that the outer portion of the skin, the cuticle or epidermis, is being continually shed and replaced ; the hair, again, is cast off and renewed many times, and the teeth once. This is patent to casual observation. But in those structures that perish and are restored particle by particle, the change eludes direct observation. Yet it is not more true that we have a second set of teeth, or from time to time new hair, than that we have often, much oftener, formed, though in a more gradual and subtle way, new muscles, new nerves, new hearts, and new brains.

If, then, waste is in proportion to work, the rate of life of the several structures or organs must depend on the activity of their function, and so must vary very widely. Compare, for instance, in this respect, muscles and nerves on the one hand with bones and ligaments on the other. The contrast between them is shown alike in their different degrees of vascularity, or in the proportion of blood that they re-

RELATION BETWEEN STRUCTURE AND FUNCTION. 43

ceive, and in the relative amount of the products of their waste. But it is not only that the rate of life of the various structures is naturally very different, but also that the rate of life of the same structure or organ varies widely in different persons and at different times, according to the conditions under which it exists. Witness, for instance, the different rate of life of the musclies of one who spends the chief portion of the day in manuai labour, or some other form of active exercise, with another who passes the whole day in sedentary pursuits. No doubt, even under con- ditions of most absolute rest, some amount of change — some degree of waste and repair — is always going on; but this must form but a small fraction of that which is involved in energetic exercise. And what is true of muscle is also equally true of, although, for plain reasons, it may be less strikingly shown in, brain.

The fact, which is generally understood, that the efficiency of the several organs, their health and vigour, depends on their thorough exercise is founded upon sure and satisfactory evidence. But more than this : in healthy nutrition the supply is in proportion not only to ordinary demands, but within certain limits to extra- ordinary ones. For as in deficient exercise there is diminished consumption, and the supply is accordingly reduced, so extraordinary activity involves additional waste, and this is associated with equivalent repair. So when structures are maintained in a state of extraordinary activity, provided only that the exercise be healthy, they not merely maintain their condition, the increased consumption is not only met by an equivalent supply, but the additional demand, by stimulating vital activity, leads to a supply beyond the waste, so that the structure becomes augmented in bulk or weight, and thus more equal to the task assigned to it. Take the muscles of the arms of a blacksmith, or of the limbs generally of an acrobat, as examples of this. And with this increase of substance is often associated an improvement in the quality of a structure. Thus, such enlarged muscles are often of a more ruddy colour, and obviously firmer than others.

The pathologist is familiar with still more striking illustrations of the same fact. Let one suffice. The heart effects its purpose of circulating the blood by the contraction of the muscular walls of its several chambers, certain valves, or flood- gates, being interposed to regulate the direction of the stream. Now, when these valves are damaged so as to become less efficient, the blood may either be obstructed in its progress or allowed to regurgitate. In either case a difficulty arises, which, in order that the circulation may be maintained, must be overcome. To do this, the heart is called on to make unusual efforts ; it must work harder. In most cases it does so, and thus in time grows larger and heavier and stronger. This, in such a case, is not disease, but, on the contrary, is in itself a conservative change, adapted to compensate a difficulty which disease has set up : a salutary effort of nature to avert an impending catastrophe.

So deficient exercise, want of use, leads to wasting, to loss of bulk or weight, and often to corresponding impairment of quality. Look at the muscles of a limb, otherwise healthy, that from accident, in which they are not directly involved, are debarred from exercise ; how they gradually, yet perceptibly, waste away, so that at length, when they are once again set free to work, they prove unequal to the slightest effort.

44' INTRO D UCTOR Y.

This law, that tho state of health and vigour of a sti*ucture is determined l)y the conditions under which it lives, holds good with all our organs. Just as manual labour or repose affects our muscles, and even, though in a less degree, our bones, 80 is the condition of the brain improved by mental work and impoverished by idleness. Thus, the bmin of the sluggard will inevitably degenerate, while no one can be awju*e of what he can accomplish until by a system of active and sustained exercise he has i*aised his mental jwwers to their highest degree of ethciency.

Herein consists the chief advantage of education over and above the actual knowleilge which is thereby acquired. It is the means by which the mental faculties are not only trained and disciplined, but evoked and cultivated. Its end is not merely the attainment of so much knowledge, but rather the development of mind force.

Not only do the sevei-al organs vary widely in degree of vital activity, but the rate of life of the body as a whole is very different at different periods. All are familiar with the contrast in this respect between youth and old age. All vital changes are most active during the earliest years, and they diminish in rapidity as age advances. During childhood there are growth and development ; then during what is called the prime of life, for the most part, simple maintenance ; at length, in the decline, wasting and degeneration. Observe the difference between growth and development and between wasting and degeneration. Growth and wasting, which ai*e opposite conditions, refer to quantity only. In growth there is simple increase of bulk or weight; in wasting there is simple loss of it. Development and degeneration, which are also opposite conditions, refer to quality. In develojv ment there is improvement in the structure of a part ; in degeneration the reverse. Growth and development may be, and often are, concurrent, as in the progress of an individual or organ from infancy, or its lirst formation, to the adult condition, or its state of higher perfection ; but they are by no means necessarily so. Organs may simply increase in bulk and weight, in quantity, without yielding any evidence of corresponding improvement of quality, as, for example, bones and muscles. Or development may proceed without concurrent growth ; nay, with even diminution of weight and bulk. Thus, in the instance of a structure, in certain stages of development of muscle, while the fibre is obviously improving in quality, rapidly assuming characters which belong to the mature condition, it as rapidly suffers loss of bulk, so that a well-formed fibre will measure much less than one far behind it in development ; or, for a remarkable instance of the whole individual, tadpoles in developing into frogs lose two-thirds of their weight.

So with wasting and degeneration. They may be, and often are, as in the decline of life, concurrent; but by no means necessarily so. Either one may proceed without the other. The causes that determine which of these changes shall occur are at present somewhat obscure, but the common cause of either or both together, when premature, is want of due and proper exercise.

But during life there is a power beyond all forms of ordinary nutrition, whether it be presented as simple maintenance or as growth and development : a power beyond all this, whereby unusual demands may be supplied, extraordinary losses may be met — the power of repair. We are wont to dwell on the wonderful

THE POWER OF REPAIR. 45

aciaptation of means to ends everywhere visible in our structures and functions. We are lost in admii'ation at the marvellous manner in which the wear and tear of our organs is met by immediate renewal. What must we, then, think of this process of repair ? It is not enough that the usual demands of the system should be fully provided for ; that natural, daily, hourly, constant losses should be sustained and compensated : there is, as it were, in anticipation of mischief, of injury or disease, by whatsoever cause produced, a power in reserve, by which the loss may be restored or the damage repaired. This power, with which all living beings are fore-armed, varies widely in its degree in different cases.

There is a vast and signal difference in the effect of injuries upon the lower, or simpler, and the higher, or more complex, animals. Thus, the simplest forms of life will survive mutilation to any extent ; nay, each fragment, possessing in itself the conditions of life, will presently become a new creature. Thus, a natural process may be rudely imitated by the artificial division of polyps and worms. But as the scale of life is ascended, as the principle of division of labour is carried out, and the several functions and structures become separated and limited, the power of reproduction is gradually reduced ; it is confined to legs or tails, or other appendages, as in tritons and lizards ; until at last in man it becomes in comparison very insignificant. With few and slight exceptions, the reproduction of lost parts is no longer witnessed ; for the most part there is only more or less imperfect repair.

Tliis remarkable difference in the repair of injury is observed not only between different animals, but also in the same animal in the course of its development, and for really the same reason. The capability of reproducing lost parts, whether in the case of the whole animal or of any particular structure, appears to exist in an inverse ratio to the extent and nature of the changes through which it has previously passed. So, as a rule, the degree and rate of reproduction varies indirectly as the age ; sometimes it is only in the very young that any reproduction occurs. Every one knows that children recover from and repair injuries much more rapidly and completely than adults. Children will go through so much because they have gone through so little. The old, for the most part, can bear but little in addition to what they have already gone through. Surgeons, guided by this, do not hesitate to adopt plans of treatment in children which they would not venture to practise on those advanced in life.

This gradual decline of a power in reserve is more commonly, though less strikingly, shown in another way. One of the most constant effects of advancing age is the diminishing ability of sustaining extra exertion, or of making any unusual effort. In middle life there is a steady loss of elasticity. The structures, by custom, become adapted to certain regular movements, but resent any attempt at excess. The daily work of ordinary life is done as heretofore, without any consciousness of declining energy ; but if tempted to join in some youthful pastime, we are apt to be painfully reminded that we are no longer young. Those who are not wise enough to recognise this change often pay dearly for evidence of it.

We may pursue this interesting subject a little farther, and observe that the several structures of the human body also differ widely in their power of repair after injury. Bones and tendons, for example, after being broken or divided, will

mn INTRODUCTORY.

unite 80 perfectly that some time afterward no trace of the injury can be discovered, the restoi-ation is complete ; while other structures, such as muscles, are never thoi-oughly restored, but ai'e joined again by another substance, which remains throughout life as a scar, always as evidence of the repair of, but incomplete recovery from, the injury. And when the matter is still further investigated, it appears that there is a distinct relation between the character of the stnictuiv, the mode of its original formation, and the power it possesses of reproducing lost or injured parts. The simplest structures, such as tendons and bones, which are made up substantially of fine delicate fibres, impregnated, in the case of bone, with earthy salts, and which are originally formed out of a structureless material, through a series of comparatively simple and direct changes, exhibit this power of reproduction in the highest degree. More complex structures, evolved through more complex processes, have an inferior power of renewal, until in the most elaborate sti-uctures, with the most complex mode of original development, the power of recovery from injury is reduced to the lowest degree, and takes the form only of comparatively imperfect repair. Thus, as in different members of the animal kingdom, so in various structures of the same animal there exists a direct relation between simplicity of construction, or of original development, and the power of recovery from mutilation, or of reproducing lost parts.

It is interesting to observe that, in the absence of perfect restoration, the substance, which in the instance of repair forms the scar, is composed of simple fibrous tissue, very like the structure of tendon or ligament. These scars, which may be very easily studied in the skin, where they are common and obvious, undergo, subsequent to their formation, important changes. The new substance becomes consolidated ; it grows firmer and denser, and gradually contracts. By this shrinking it becomes very much reduced in size, and the structures to which it is attached are drawn in. Thus, when a scar is examined many months after a wound has healed it is found to occupy only a fraction of its original extent; and if at first extensive, the adjacent skin is displaced, and for some distance is made tense by being stretched. In extreme instances, where the previous loss of substance has been great, as after severe burns, the persistent and powerful contraction of the large scars often in this way produces dreadful deformity, and by limiting their movement, very seriously interferes with the use of the limbs.

But although in this way scars tend for a very long period gradually to grow smaller, yet from another cause they are subject to increase. A scar on a small child grows with the growth of the whole body, so that in the course of years it may extend considerably : in fact, it has become a part of the body, and subject to the laws which regulate the growth of the natural structures.

Thus, then, different degrees of life belong to different periods of it. The seven ages of man — infancy, childhood, youth, adolescence, manhood, decline, senility — may for physiological purposes be reduced to three — growth and development, maturity, decline. These are distinguished by the relative degree of the constructive and destructive processes. In the first, constructive changes are in excess ; in the second, constructive and destructive changes are balanced ; in the third, destructive changes are in excess. But they are distinguished also, and in

BATE OF LIFE. 47

this more, by the relative rate at which these changes simultaneously proceed. In early life the vital processes are most rapid, and they gradually slacken as age advances.

Once more. During the course of life different organs and systems of organs attain their most perfect condition at different periods. An illustration of this, in a general way, is presented by what are called the vegetative and animal functions. The former are in full and complete operation long before the latter. Another appears in the case of certain glands, which attain to maturity on^ after another. But a more familiar instance is seen in the organs of the senses and of the intellect. It is very well understood that the senses are possessed in all their acuteness before the intellectual faculties are fully developed, and the senses fail before the intellectual powers decline.

Furthermore, there can be little doubt that the rate of life or of tissue-change varies in different persons, and the extent of this variation is characteristic of human nature. Animals are less eccentric than man. In their physiology, instances of individual excess or defect do not so commonly appear as in him. In them, too, each organ is more accustomed to go constantly in harmony with the rest. The whole are active or the whole are indolent. Man, although, of course, his various organs hold the same physiological relation to each other, differs in this respect in a singular degree. Various temperaments, individual idiosyncracies, characters distinguished from others, are far more marked among men. Allowing fully for imperfect obser- vation, we are less alike than are animals. And what is true of different men is true, in a less degree, of different organs of the same man. Activity of body and of mind are in him, by no means, in such constant accord as in animals. The impression is general that, as a rule, the size of the brain and the mental power of an individual are in proportion : that a man with a large brain has more mental capacity than another with a small one. Why this rule is so frequently broken, is subject to such numerous exceptions as to render any inference of intellectual power drawn from the size of the head or brain a very uncertain one, is not, perhaps, so difficult to explain if the question of rate of life or of tissue-change be taken into account. The vital activity of the organ, or its rate of change, is a factor that cannot be so readily or accurately reached, but, nevertheless, this which is involved in the nature of the constitution, or temperament, or idiosyncracy, has to be considered. Is the whole man, or his brain, quick or slow, lethargic or energetic %

How strikingly is this illustrated by the influence of age ! How marked are the different degrees of cerebral activity at different periods of life ! How quick the apprehension, how vivid the imagination, of the young ! How prone the perceptive faculties are to grow dull as life advances ! Of course there are other changes, for the most part of greater importance, which more than compensate these, and other influences which come into play. But, so far as simple rapidity of function is con- cerned— mental activity — the contrast between the young and old is obviou's. Even a very few years are apt to produce a considerable difference in this respect. Those who have had much experience in the conduct of examinations, especially of com- petitive examinations, are probably aware of this. The older men, notwithstanding many advantages on their side, such as a longer period of training, a larger amount

4B JNTROD UCTOR Y.

of work, i)erhaps a wider range or greater depth of study, do not, as a rule, come out higher thtui the younger ones. Of course, one cannot pretend to be precise in such a statement as this ; tliere are circumstances outside the present question to be taken into consideration. But the objection often urged, that it is unfair to allow older men to contend with younger ones in competitive examinations on the score of their supt^rior advantages, is met by the fact that the younger men, at least, can hold their own in the struggle, and this chiefly because of the quickness of their work. They can think better against time.

Although to many the illustration is not so familiar, it is oftentimes still more striking in cases of illness. In convalescence after fever oji other grave disease, in which the powere of the system have been taxed to the uttermost, the exhaustion of the higher nerve-centres is often shown in various ways ; but, perhaps, in none is it more i-emai-kable than in the sluggish flow of ideas through the mind. Questions are cleai-ly.but slowly, understood, and at length intelligently answered; as well answered, perhaps, as they could be in perfect health, but then, so much more time is taken up by the efibrt. The conversation must be carried on deliberately. Even ordinary rapidity of utterance on your part will cause distress, and you must wait patiently, sometimes even for a long while, before the answer comes. But as the blood and its circulation is restored, the stream of thought quickens, until it flows again as brightly as ever.

We are, indeed, but too familiar with another illustration of the same fact in the vast difierence which may be so frequently observed in the mental activity, or rate of work, of the same brain. How widely various is the productiveness of the same organ at different periods ! Think, for a moment only, of the effect of quickening the cerebral circulation, or increasing its supply of blood, by the use of a stimulant. Under this spur, with what a spring will a languid and exhausted brain start forward into rapid and energetic action ! Much is revealed by the influence of a glass of wine upon the flow of ideas.

But beyond this, there is a consideration of far more importance. In man, the state of the brain in this respect varies, it may be repeated, in a singular degree. Its rate of change can hardly be judged of by that of the body generally. Other organs may be active, and this idle, or this may be full of life, while the rest are indolent. Necessity, will, habit, external influences, accidental associations, and a host of cir- cumstances, come in here. Hence the important part played by the constitution, or tempei*ament, or energy, or activity, in the duration of life ; whether the fire con- sumes slowly or bums intensely. Thus, some who have had the fullest opportunity of forming a sound judgment on the matter have been disposed to believe that, as a rule, there is a direct relation between the habitual slowness of the pulse and the duration of life ; and although more numerous and exact observations on the subject are wanting, the view is, to say the least, a very reasonable one. But it is not a question of the consumption of every part. The duration of life is rather to be measured by the rate of life of the most active of the vital organs. Just as the strength of a fortress is only the strength of its weakest part, so it may be said that the term of life of an individual is only the period of duration of that vital organ which is worn out soonest And thus we can appreciate not only the point, but the

BRAIN WORK, 49

•weakness of the comment attributed to Swift on hearing some one speak of a fine old man : " Nonsense ! If his head or his heart had been worth anything, they would have worn him out long ago ! "

Most people, no doubt, have some amount of brain substance in reserve : that is, they never get the best they can out of what brain they have. For one instance in which the brain is overworked there must be many hundreds or thousands of cases in which it is not used enough, even for the ordinary conditions of health. Yet the laws of nature are inexorable, and in this case the penalty paid is heavy for any attempted violation of them. For the brain, as for every organ, exercise, a due amount of it, at least, is a condition of health, "Waste or disease is the conse- quence of extreme idleness. For other vital organs nature insists on due and proper work. We cannot, if we will, make the heart, or lungs, or spinal cord altogether idle. Their regular work is determined beyond our rule, as a condition on which life itself immediately hangs. The higher part of the brain — the cerebrum — is more within our control. But to what degree ? Not so far, probably, as is often imagined. Can we make it altogether idle in the physiological sense 1 Can we completely rest it, except in sleep, even if we try 1 Is not its activity also, within wide limits, an im- perative condition 1 After all, we can only determine, for the most part, in what way it shall be active. If not used worthily, it must be employed unworthily. It is an old remark, that persons who have nothing to do are often the most busy : that is, when the brain is not occupied on important subjects it employs itself on trifles. In animals of the same species, it is probable that the quality of the brain-work does not vary widely ; but among men brain- work differs far more in quality than in quan- tity. Most men, for some portion of the twenty-four hours, are " up and doing." But doing what 1, The grades of cerebral activity are infinite. In this organ, it does not appear to be so much a question of rest and exercise as to what purpose the activity which is imperative shall be turned. Dr. Watts, from another point of view, long ago, made this idea famous.

Then there is the all-important question of culture, the increase of power by constant healthy exercise, which has been already alluded to, increase of size, to some extent, but still more, no doubt, increased facility of change. So that it comes to pass that in the end mere mass has not much to do with the result. It is super- seded by motion ; and the fact is too familiar that the work of a large or heavy brain out of condition is nowhere in the race against the energy of one much less that has been diligently cultivated. So far as simple activity of intellect is concerned, the in- fluence of practice or exercise is often strikingly shown in the contrast of the mental state of individuals in cities and in rural districts. Widely difi'erent is the usual rate of thought in the two cases. Every one can recall conversations with uneducated persons in various places which illustrate this. It may be said, indeed, " All other circumstances being alike, the size of the brain appears to bear a general relation to the mental power of the individual." But when are all other circumstances alike?

As the amount of work done cannot be reckoned from mere bulk of body, so life cannot be estimated by mere number of years. It must be known also how mUch of life there has been in each year. Neither could it be told simply from the size how 4

60 INTRODUCTORY.

much work a brain has done, or can do. It would be necessaiy to know how long it can work, and how much it can do in a given period. It is always a question of rat<> into time.

Sleep. — Action involves destruction. The discharge of function implies the consumption of structure. Rest is necessary to repair. Therefore, alternate periods of activity and repose are common to all living structures. For it is evident, in order that the condition of an organ may be maintained, this waste must be repaired, and the repair must be equal to the waste, the supply to the demand.

The certain fact that active exercise is destructive of substance does not preclude the possibility that, even during its continuance, repair may Se to some extent proceed- ing simultaneously with the waste, but it does involve the proposition that during active exercise the amount of waste exceeds that of repair. Therefore, in order that the waste may be repaired, that the condition may be maintained, there must be periods of comparative inactivity, of more or less complete repose.

If active exercise could be continued without intermission, it would at length weai* out the structure, and the limit to its duration is, no doubt, associated with the amount of tissue consumed. Thus, the sense of fatigue in muscles may be due to the want of balance between waste and repair. Exercise, therefore, is followed by repose — the period of renewal ; and when this is accomplished, the body is once again in a condition for active exertion, which must at length, in turn, be succeeded by repose. Thus, then, there must be, as the condition of vital action, alternate periods of exer- cise and repose. The intervals vary widely in different cases, but both states are natural to all structures, and necessary to their health.

Hence, the need of sleep — that is, a season of rest — arises from the excess of the waste of certain nerve-centres over their repair during the hours we are awake. But complete and prolonged repose, or abeyance of function, of some nerve-centres is incompatible with life. The spinal cord and medulla oblongata, for instance, like the heart and some other parts, must be restored through intermittent periods of com- parative repose. It has been forcibly said that the true spinal system never sleeps. There is not, however, this immediate necessity for the sustained activity of other portions of the nervous system, and so these yield to rest more profound and pro- longed.

Sleep is especially rest of the brain — of the sensorium and cerebral lobes. Its leading phenomena are the result of the more or less complete suspension of their functions ; for sleep is the suspension of consciousness and of the mental faculties generally. Sleep is to the brain what repose is to every other organ of the body. While, therefore, all living beings, all organs and structures, rest at intervals, those animals only which possess a brain, and are endowed with consciousness, can be proi)erly said to sleep.

The sleep of plants is often spoken of. But it cannot be correct to say that plants sleep, if sleep be understood in the sense in which it is generally, and here, employed, to imply a state of unconsciousness, and of suspension of other faculties which depend on the activity of the highest nerve-centres. Taken thus, in its common and proper sense, neither plants nor the lowest animals sleep, because they are not endowed p^ith

DREAMS. 51

the organs whose state of rest is sleep. But plants and all living beings exhibit periods of repose or comparative inactivity.

A great deal has been said about the circulation of the brain during sleep, and very opposite opinions have been expressed. In this, as in perhaps many other cases, analogy is too often overlooked. There is no reason to suppose the brain to be an exception to what appears to be an universal law ; that the circulation in an organ varies with its activity. That during the repose of the brain its circulation is correspondingly reduced is the conclusion to be drawn from the eflfects of rest on other structures, and this conclusion is supported by direct evidence.

And it must be understood that the diminished supply of blood to the brain during sleep is the consequence, and not the cause of, the state. The supply of blood to an organ depends on its wants, not its wants on the sup])ly. Increase the activity of an organ, and its circulation is increased ; diminish its activity, and its circulation is diminished. The supply is regulated by the demand.

Sleep, of course, like all other forms of rest, varies widely in degree. It may be so light as to mean no more than a passing reduction of activity, mere drowsiness ; it may be so profound as to consist in a complete suspension of all those functions which depend on the nerve-centres within the skull.

Dreaming and Somnambulism. — Much light appears to be thrown on the physiology of the higher nerve-centres by the study of the curiously interesting conditions of dreaming and somnambulism.

When sleep is partial or imperfect, the functions of those ganglia whose rest is sleep will not be entirely suspended. They will remain more or less active. Impressions will still be recognised by the hemispheres, and will give rise to ideas. Thus, dreams are produced. Dreams, therefore, are the result of imperfect exercise of the hemispheres when in .a state of partial repose. There may be total absence of consciousness of external things, and yet withal a state of mental activity, varying greatly in degree and duration. It may be so slight and transient that nothing more than shadowy and evanescent images float from time to time across the mind, leaving no trace upon the memory. It may be so energetic that impressions produce the most vivid, definite, and enduring pictures. It is not at all uncommon, indeed, for impressions in these circumstances to produce ideas more freely and powerfully than in the waking state, inasmuch as they are not inter- rupted by the intrusion of external circumstances, whose influence is at the time shut off". Dreams, then, occur when sleep is not profound. They cannot arise during complete repose. There is no sufficient reason to deny the existence of a period of complete unconsciousness, of complete suspension of the mental faculties. Doubtless the brain, like other organs, is at times in absolute repose. "While dreaming, sleep must be considered imperfect.

Again, if the general view here expressed be the correct one — that dreaming is the natural condition of imperfect repose — there is no good reason for denying the supervention of dreams at any period of sleep. It has been a favourite doctrine with some, with one illustrious man especially, that drearils occur only during the period of waking, that they are peculiar to the period of transition from sleep. But it seems to be more consistent with knowledge and observation, as, for

n INTRODUCTORY.

instftnoe, with changes of expression in sleep, to believe that they are not necessarily confitietl to the waking state, but rather that they may arise at any moment when sleep is not profound

In a healthy state, and in natuml circumstances, however, sleep will be profound or prolonged according to the degree in which the brain has Ijeen fatigued by i)revious exertion. But as the brain becomes refreshed the want of rest is retluced, and sleep gi-adually becomes lighter. Hence it is that towards the termination of our slumbers we are apt to dream most vividly and coherently. Hence the adage that morning dreams are true.

There can be little doubt tliat dreams are very transient, but the evidence of the extreme rapidity which has been assigned to all of them is defective. The idea that they are almost instantaneous is connected with the one just alluded to, that they are limited to the waking state. Of course, the duration of dreams bears no conqmrison to that of the events and circumstances which they picture, but looking at the relation of dreaming to somnambulism, their frequent concurrence, the period occupied by day-dreams, and the time that disturbed sleep and other indi- cations of dreaming will sometimes last, it is jjerhaps more reasonable to conclude that some dreams are not so instantaneous, as many imagine.

It is highly probable that all animals with cerebral hemispheres dream. This conclusion, which naturally follows on the view here taken of the nature of dreams, b confirmed by observation. For example, dogs will growl, snarl, and snap, whine, and wag their tails, or prick up their ears in sleep, and start up suddenly in alarm, as if in danger, without any external cause. Lucretius (De Rerum Natura, Liber IV.) describes minutely the indications of dreaming in the lower animals.

When impressions reach the cerebral hemispheres, they arouse ideas. Impres- sions may be objective — arising from without, what we call real ; or subjective — arising from within, what we call fancies. The exciting cause of dreams, then, may come from without, and this would imply some degree of activity of the sensorium ; or from within, for it is only during complete sleep that the cerebral lobes are quite inactive. As during the waking state we cannot obliterate ideas, although in dark- ness and silence all external sources of impression may be removed, so when sleep is not profound, and the cerebral lobes are in some degree active, dreams more or less vivid must occur.

As the chief feature of sleep is a state of unconsciousness, so the remarkable feature of dreaming appeai-s to be an absence of the power of the will over the current of thought and over action. Thus, ideas are aroused in rapid succession with- out guidance or correxition, and no volitional acts are accomplished. Hence the fre- quent incoherence and inconsistency of dreams. Of course, there are all degrees of this. Dreams may be, and often are, consistent and rational, whether from the more complete exercise of the cerebral lobes, or from the nature of the impressions which excite them ; but oftentimes they are characterised by a strange want of regulation and co-ordination of the ideas which represent them. And of what slovenly patch- work are our dreams sometimes made up ! A fragment of our waking thoughts here, another there, fantastically put together into an utterly unreasonable, yet in some sense an intelligible whole. When such a dream is remembered, it is curiously inte-

DREAMS. 53

resting to trace back, as we often may, various portions of it to their respective sources, to recall the actual scenes or mental visions whence they have been derived.

When, therefore, we dream what we cajl nonsense, it is because there is a partial or complete absence of voluntary control over the current of thought, and because we cannot compare our conceptions and ideas with surrounding objects and circum- stances, and thus correct them.

The extent to which the ideas that constitute dreams are coherent probably de- pends, in great measure, on whether they are habitual or strange to the waking state. When the will is not alert, old ideas are more apt to be orderly than new ones, for the former may fall into their accustomed sequence, whereas the latter have not even habit to arrange them. Every one knows how an idea excited by an impression may forthwith arouse a train of others which have been before associated with it ; how, in this way, by some object that catches the eye, or by some sound that strikes the ear, we are carried back to past scenes which have long since been forgotten. In such a case, we know also that a distinct effort of the will is often needed to recall the truant mind to present affairs. Thus, for the most part, dreams are coherent and rational in proportion as they arise out of existing circumstances. The wildest and most absurd ideas result from some temporary disturbance of some function, or from some local or general discomfort. And it is instructive to remark that when, in dreams, probabilities are violated or possibilities disregarded, the ideas are usually of such a nature that we can, when awake, correct them by the influence of surround- ing circumstances, such as those of time and space.

In comparing, then, the condition of the mind in dreaming with its active state while awake, we are led to notice these distinguishing features : — The will is in abeyance ; it ceases to control, or rather to direct, the current of thought ; the cor- recting influence of external impressions is suspended.

Impressions conveyed to the brain, when awake, excite ideas which are for the most part, in a healthy mind, subjected to the regulating influence of the will ; and if they give rise to acts, these are voluntary and rational. But when the influence of the will is suspended, and it ceases to direct the current of thought, the acts which such ideas thus produced may at once excite are often strikingly irrational or alto- gether absurd. Such examples may be seen in persons intoxicated by alcohol, chloroform, ether, or laughing-gas. This condition is hit in the drunken Cassio, when he is represented stumbling on to his knees, and then, the attitude suggesting the idea, beginning to pray. So, again, we often observe sight, sound, or touch start- ing a current of ideas in one under the influence of ether or chloroform. And it is interesting to note that these impressions do not, for the most part, evolve correct ideas of the real circumstances of the case, because they are unusual ones, but they are interpreted according to the habitual circumstances in which they are experienced. In vino Veritas.

As in these cases, so and in the same way it is doubtless possible sometimes to lead the ideas during sleep, when not profound, by means of external impressions, and even to determine their nature. Thus, gloomy ideas may be suggested by a dull tone of the voice, while cheerful ones may be aroused by lively sounds. In

W INTRODUCTORY.

the same way also, tlie ideas may be adapted to the circumstances in which a person may be placed. Every work on the subject contains some illustrations of this.

And, just as a dream may be started by an external impression, so an impression made on any of the senses during a drqam will oftentimes fall into the current of ideas then flowing through the mind. Thus, a noise may become the report of fire- arms, or the shout of a multitude, or a peal of bells, or something else, according to the subject of the dream.

The nature of di-eams in their relation to the absence of the correcting influence of impressions from without is well illustrated by the efiect of darkness and silence on deliriimi. The phantoms which then arise will often at once disappear in the presence of light or at the sound of a well-known volCe. And here it may be observed that, in proportion as the mind is uncultivated and barren, with but scanty stores from the past to feed on, or undisciplined, the will being feeble and powerless to direct the thoughts or to regulate the ideas, so it is dependent on a constant supply of external impressions and on surrounding objects. The oppor- tunity for reverie and abstraction which the poet and philosopher anxiously solicit and joyfully embrace, the ignorant and idle dread and shun. Hence the disastrous effects of solitary imprisonment appear to be in proportion to the want of mental culture in the victim.

There is a peculiar condition of the mind, often occurring in some persons, which is well expressed by the phrase day-dreaming. In this state the ideas are allowed to flow on without control They are not restrained by any effort of the will ; in the worst form they are not even co-ordinated. One idea suggests another, and so on, until the thoughts have wandered far away from the original subject. Nothing is seen but the visions of fancy. The' most improbable, nay, impossible, prospects are conjured up, and contemplated either as present or future realities, and no attempt is made to check or control the most extravagant or erroneous conclusions. Here, however, at least, at the outset, there is an indisposition rather than an inability to reason. When in this state, a person is said to build castles in the air. The mind is wholly withdrawn from the consideration of external and surrounding circumstances, and revels in the luxuriance of its thoughts. This is really a dreaming state, although, owing to the activity of the sensorium, day- dreams are more readily corrected by external circumstances.

What are called imaginative minds are most subject to this condition, which must be regai'ded as an unhealthy one, for if not resisted, but allowed to increase, it may weaken the intellectual, the reasoning powers, and otherwise impair the mind. " All power of fancy over reason," says Johnson, in his characteristic way, " is a degree of insanity. By degrees the reign of fancy is confirmed. She grows first imperious, and in time despotic. Then fictions begin to operate as realities, false opinions fasten upon the mind, and life passes in dreams of rapture or of anguish."

The imagination and the reason are in great measure antagonistic faculties. Perhaps they are never found highly developed together. It is only when the imagination is stronger than the reason that it can escape from its control. When the latter predominates, the former is held in check. No author has set this forth more clearly and vigorously than Lord Macaulay, who has handled the subject in

DAY-DREAMS. 55

more than one of his essays. In that on Dryden especially, he says the imagination is never so strong as in people incapable of reasoning. With striking force and felicity of illustration, he shows how, in the development of the reason at the expense of the imagination, "the progress of a nation from barbarism to civili- sation produces a change similar to that which takes place during the progress of an individual from infancy to mature age." " Our judgment ripens, our imagination decays." " Such is the law of our nature." He points out also the analogy in the triumph of the imagination over the reason between savages, children, madmen, and dreamers.

Some persons are almost always dreaming, even when awake, and this constant day-dreaming seems to be, at all events, incompatible with a well-disciplined mind and a strong will. Coleridge may be mentioned as a conspicuous example.

Indeed, if we attend at all to the state of our mind, we must observe that it varies widely ; and during a considerable portion of our waking hours, in many persons, especially in the young, its condition is not far removed from that of day- dreaming. When we are not at work, when the attention is not fixed, during periods of leisure, the intellect is wont to escape insensibly from the dominion of the will, and to wander far on into the regions of thought, one idea suggesting another, which forthwith takes its place. One step farther, and the influence of surrounding circumstances is almost shut out, and the imagination revels without restraint. Then we may be said to dream.

Day-dreaming, or reverie, and the dreams of sleep are connected by a peculiar phase of dreaming, which sometimes occurs when the sleep is unusually light, or more often when we are awakening out of sleep. In this state the sensorium is more or less active ; we are conscious. It is characterised, moreover, by a partial and imperfect control over the current of thought, and a voluntary efibrt, in some degree successful, is made to prolong agreeable ideas and to dispel gloomy ones. This condition, oftentimes very pleasant, must be familiar to every one, as occurring at the dawn of day, before rising.

Again, every one knows that a dream out of which we have awakened is very liable to recur if we soon fall asleep again. We dread this recurrence when a dream has been horrible, or court it when a delightful vision has been interrupted. Such cases tend to establish the relation between our sleeping and waking thoughts. By watching and analysing the phenomena, we can observe how insensibly they pass into each other, the vision of our sleep rising into ascendancy as the influence of external impressions and of the will is withdrawn.

The supremacy of the will, in its relation to the intellectual powers, * is the best

*We say the will in its relation to the intellectual powers, for distinct and widely different acts are commonly included in the operation of the will. The will is referred to in relation to certain forms of muscular action. We speak of voluntary or volitional acts, meaning that these are determined by the will. Again, we speak of the will as governing, in a greater or less degree, the operations of the intellect, as directing thoughts, regulating the ideas, controlling the imagination, and so forth.

Surely a distinction ought to be drawn between the power of the will in " determining certain actions of the body and the influence of the will in its relation to the faculties of the mind. Is the power by which certain movements are determined identical with that by which the various

66 INTRODUCTORY.

indication of a healthy mind, and ftiilui'e of the power of the will is tlie earliest and most obvious symptom of mental defect or debility. As by the presidency of the will man is distinguished from animals ; so do men differ widely in the degree to which tlie power of the will is developed. In any case, it may be said that when the will is strongest, when its influence over the intellectual faculties, as well as over the ptissions and emotions, is greatest, the mind is in its most efticient state. Now, the remarkable analogy between the mental phenomena in dreaming and insanity lias not been overlooked. As in dreaming, so in insanity ; the power which the mind in a healthy state possesses of directing and controlling, within certain limits, the current of its thoughts is to a greater or less degree lost. And the ideas and imagination which thus run riot, as it were, are not corrected or checked by the influence of external things through the senses. There is, however, this difference : in dreaming, the senses are more or less closed ; in insanity, these paths to the mind are still open, but the disordered intellect ignores the evidence which they convey.

In reverie, the same condition to a great extent prevails. It is most common and intense in minds in which the emotions and imagination predominate. In the state called abstraction there is, however, this difference ; that whereas in either condition the influence of external impressions is for the time ignored, in reverie the will is in abeyance, in abstraction it is dominant ; the will has, as it were, the intellectual powers well in hand. A train of thought is guided without interruption to a logical conclusion, and therefore this condition is eminently favourable to sound and sustained reasoning.

The sense of fatigue that follows upon great mental exertion seems to be in proportion to the effort of the will which has been necessary to accomplish the task. As with manual, so with mental labours : those which are executed with the least effort involve the least fatigue. Yolitional acts, whether of body or mind, which involve intense effort of the will, produce, beyond all others, exhaustion. Thus, most men who are accustomed to task severely and exhaust their mental powers have

intellectual faculties are guided or governed ? It has been said, '* We have in our own consciousness of effort, and in our experience of subsequent fatigue, a very strong indication that the power which thus controls and directs the current of thought is of the same kind with that which calls forth volitional movements of the body, though exerted in a different mode," But is the indication thus afforded strong enough to meet the evidence which tends to establish a distinction ? There appears to be no correspondence between the power of the will in its relation to the body and to the mind. Man is pre-eminently distinguished from all animals by the power of his will over the operations of his intellect ; wheresis in the power of the will over the muscles, in various voluntaiy acts, he is inferior to many. Just as in children, savages, madmen, and dreamers, so in the lower animals ; there seems to be great deficiency, or almost total absence, of the power of the will, not over muscular movement, but over the current of thought. "When animals are said to be deficient in will, this is true in relation to the mind only. To deny them the possession of a strong and vigorous will in relation to muscular action is to put forth a mere dogma in opi>osition to the most obvious and familiar facts. How can it be reasonably asserted that animals are incapable of intensely volitional acts ?

So, among different men, and even in the same man at different periods of his life and in different circumstances, there is no direct relation between the power of the will in its influence on the body and on the mind ; indeed, oftentimes rather an inverse one.

At all events, the word will, as currently understood, includes the power by which certain acts are determined, and the faculty by which the various operations of the intellect are co-ordinated and governed.

SOMNAMBULISM. 57

experienced at times a temporary failure of the will to control and direct the current of thought. For a few moments there is an utter inability to concentrate the a-ttention on a particular subject. There is, as it were, a mental struggle before the purpose is accomplished. This is a strong hint to rest awhile.

All forms and degrees of mental activity exist, from intense voluntary thought, or the clearest and profoundest reasoning, to the wildest insanity or the most in- coherent dreams.

Now, just as the dreams may be regarded as due to partial activity of the cerebral lobes when in a state of imperfect repose, so may the condition termed somnambulism be regarded as essentially the result of a state of more or less complete activity of the sensorium, the hemispheres beyond being nevertheless at rest. In what may be X3alled the purest form of somnambulism, various acts may be accomplished in the most perfect manner as the direct result of impressions, without any evidence of the intervention of ideas.

But, although in somnambulism impressions do not necessarily arouse ideas, yet they nevertheless produce sensations and determine sensori-motor acts. That they reach the sensorium, and are not merely excito-motor in their nature, is evident from their results. Sounds are sometimes heard and objects recognised by the sight and touch.

The term somnambulism appears to be very loosely employed. In its most xjommon acceptation, a combination of dreaming and somnambulism is implied. Perhaps, indeed, this is the most common form of somnambulism. Not only is the sensorium active, but the hemispheres themselves are partially awake. A common instance of this is "talking in sleep." What is called nightmare is an ugly form of this combination, and it is instructive to notice that this usually depends on some eccentric and morbid irritation, as indigestion. But it is also sometimes due to im- perfect arterialisation of the blood, and such defective action of the lungs or lieart is .a common cause of the wildest and most frightful dreams, of what may be truly called delirium in sleep. Although the description usually given of somnambulism would imply an active state of the cerebral hemispheres as well as of the sensorium, would include a state which is essentially that of dreaming — so that somnambulism has been described as an " acted dream " — yet, while it may be admitted that this more complicated condition may be a common one, it is important to recognise the fact that a state may occur in which some or all of the sensorial centres are active, the cerebrum itself being nevertheless in a state of complete repose, the actions which result being simply sensori-motor, or instinctive ones. Thus, no ideas are aroused and nothing is remembered. This may be described as the simplest and purest form of somnambulism.

It seems, then, that the clearest and most correct idea will be obtained of these two states, and of their relation to each other, by regarding them as manifestations of various degrees of activity of those centres which in profound sleep pass into a state of complete repose ; that either alone may be active while the other is at rest ; or both together, in imperfect sleep, may exhibit all degrees of partial activity in various proportion, short of that thorough and complete exercise of their functions when wide awake.

8B INTROD UCTOR F.

It appears that this yiew will afford an insight into certain facts which do not otherwise admit of explanation. For example, dreaming is more frequent than som- nambulism, because, of all portions of the nervous system, the cerebral lobes are the most sensitive to variations in the quantity and quality of blood circulating through them. Witness the effects of alcohol, ether, and chloroform. Again, somnambulism is more common in the young, because then the sensorial centres are more prone to activity. With regard to dreams, the rule is less general, being influenced by habits of mental exercise. Again, the remembrance of dreams, not of somnambulistic acts : it is important to note the absence of memory in somnambulism. It would appear that acts purely somnambulistic are never remembered or recalled. This seems to point to theii- nature. They find their parallel in instinctive actfons. Once more, the dex- terity and accuracy of somnambulistic acts ; for example, of muscular movements in walking. Perhaps, in this case the cerebellum is awake also. The somnambulist walks across a narrow plank over a frightful chasm steadily, and without fear. Why? Because the act is a sensori-motor one, and no idea is called into play. For the same reason, a person wide awake may accomplish the same feat in the same manner, if the danger be concealed from him, if he have no idea of it. In the former case, he may see it, but has no idea of it ; in the latter, he has no idea of it, because he cannot see it.

In this view of the matter, therefore, the actions of the somnambulist are essen- tially of the nature of instinctive ones. A careful analysis of them will show that they possess this character. In the simplest and purest form of somnambulism, as in the simplest and purest examples of instinctive acts, there is not any satisfactory evidence of the operation of the intellectual powers. In either case is seea the adap- tation of means to ends, but there is no evidence of the intervention of ideas, of the calculation of consequences, of reason. This difference, however, must be noted in the two cases. The operations of instinct are invariably associated with an active and acute state of the senses. In somnambulism, all the senses are not commonly in full activity. Cuvier perceived and pointed out this relation.

Summarily, then, these several states may be thus contrasted : —

In profound sleep, there are no acts beyond excito-motor ones, and even these are reduced.

In somnambulism there are, beyond these, sensori-motor acts.

In dreaming, ideas are aroused. Impressions are either subjective or objective. If the latter, it is presumed that th