Table of Contents

THE PROLONGATION OF LIFE

EDITOR’S INTRODUCTION

PREFACE

CONTENTS

THE PROLONGATION OF LIFE

PART I

II

III

PART II

I

II.

III

IV

V

PART III

I

II

III

PART IV

I

II

III

IV

V

PART V

I

II

III

PART VI

I

II

III

PART VII

I

II

III

PART VIII

I

II

III

IV

V

PART IX

I

II

FOOTNOTES:

THE PROLONGATION OF LIFE

OPTIMISTIC STUDIES

Élie Metchnikoff

1908

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Mauro Liistro Editore

© 2015 Some Righits Reserved

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e-ISBN:9783963619441

THE PROLONGATION OF LIFE

OPTIMISTIC STUDIES

BY

ÉLIE METCHNIKOFF

SUB-DIRECTOR OF THE PASTEUR INSTITUTE, PARIS

THE ENGLISH TRANSLATION

EDITED BY

P. CHALMERS MITCHELL
M.A., D.SC. OXON., HON. LL.D., F.R.S.
Secretary of the Zoological Society of London; Corresponding Member
of the Academy of Natural Sciences of Philadelphia

Originally published by
G. P. PUTNAM’S SONS
NEW YORK & LONDON
The Knickerbocker Press 1908

***
2016 Mauro Liistro Editore
Some rights reserved
***

EDITOR’S INTRODUCTION

Élie Metchnikoff has carried on the high purpose of the Pasteur Institute by devoting his genius for biological inquiry to the service of man. Some years ago, in a series of Essays which were intended to be provocative and educational, rather than expository, he described the direction towards which he was pressing. I had the privilege of introducing these Essays to English readers under the title The Nature of Man, a Study in Optimistic Philosophy. In that volume, Professor Metchnikoff recounted how sentient man, regarding his lot in the world, had found it evil. Philosophy and literature, religion and folk-lore, in ancient and modern times have been deeply tinged with pessimism. The source of these gloomy views lies in the nature of man itself. Man has inherited a constitution from remote animal ancestors, and every part of his structure, physical, mental and emotional, is a complex legacy of diverse elements. Possibly at one time each quality had its purpose as an adaptation to environment, but, as man, in the course of his evolution, and the environment itself have changed, the old harmonious intercourse between quality and circumstances has been dislocated in many cases. And so there have come into existence many instances of what the Professor calls “disharmony,” persistences of structures, or habits, or desires that are no longer useful, but even harmful, failures of parallelism between the growth, maturity and decay of physical and mental qualities and so forth. Religions and philosophies alike have failed to find remedies or efficient anodynes for these evils of existence, and, so far, man is justified of his historical and actual pessimism.

Metchnikoff, however, was able to proclaim himself an optimist, and found, in biological science, for the present generation a hope, or, at the least, an end towards which to work, and for future generations a possible achievement of that hope. Three chief evils that hang over us are disease, old age, and death. Modern science has already made vast strides towards the destruction of disease, and no one has more right to be listened to than a leader of the Pasteur Institute when he asserts his confidence that rational hygiene and preventive measures will ultimately rid mankind of disease. The scientific investigation of old age shows that senility is nearly always precocious and that its disabilities and miseries are for the most part due to preventable causes. Metchnikoff showed years ago that there exists in the human body a number of cells known generally as phagocytes, the chief function of which is to devour intruding microbes. But these guardians of the body may turn into its deadly enemies by destroying and replacing the higher elements, the specific cells of the different tissues. The physical mechanism of senility appears to be in large measure the result of this process. Certain substances, notably the poisons of such diseases as syphilis and the products of intestinal putrefaction, stimulate the activity of the phagocytes and so encourage their encroachment on the higher tissues. The first business of science is to remove these handicaps in favour of the wandering, corroding phagocytes. Specific poisons must be dealt with separately, by prevention or treatment, and it is well known that Metchnikoff has made great advances in that direction. The most striking practical side of The Nature of Man, however, was the discussion of the cause and prevention of intestinal putrefaction. Metchnikoff believes that the inherited structure of the human large intestine and the customary diet of civilised man are specially favourable to the multiplication of a large number of microbes that cause putrefaction. The avoidance of alcohol and the rigid exclusion from diet of foods that favour putrefaction, such as rich meats, and of raw or badly cooked substances containing microbes, do much to remedy the evils. But the special introduction of the microbes which cause lactic fermentation has the effect of inhibiting putrefaction. By such measures Metchnikoff believes that life will be greatly prolonged and that the chief evils of senility will be avoided. It may take many generations before the final result is attained, but, in the meantime, great amelioration is possible. There remains the last enemy, death. Metchnikoff shows that in the vast majority of cases death is not “natural,” but comes from accidental and preventable causes. When diseases have been suppressed and the course of life regulated by scientific hygiene, it is probable that death would come only at an extreme old age. Metchnikoff thinks that there is evidence enough at least to suggest that when death comes in its natural place at the end of the normal cycle of life, it would be robbed of its terrors and be accepted as gratefully as any other part of the cycle of life. He thinks, in fact, that the instinct of life would be replaced by an instinct of death.

Metchnikoff’s suggestion, then, was that science should be encouraged and helped in every possible way in its task of removing the diseases and habits that now prevent human life from running its normal course, and his belief is that were the task accomplished, the great causes of pessimism would disappear.

In this new volume, The Prolongation of Life, the main thesis is carried further, and a number of criticisms and objections are met. The latter, so far as they relate to technical details, I need say nothing of here, as Metchnikoff and his staff at the Pasteur Institute are the most skilled existing technical experts on these matters, but I cannot refrain from a word of comment on the brilliant treatment of the objection to the suggested amelioration of human life that it considered only the individual and neglected the just subordination of the individual to society. In the sixth Part of this volume, Metchnikoff discusses the relation of the individual to the species, society or colony, from the general point of view of comparative biology, and shows that as organisation progresses, the integrity of the individual becomes increasingly important. Were orthobiosis, the normal cycle of life, attained by human beings, there still would be room for specialisation of individuals and for differentiation of the functions of individuals in society, but instead of the specialisation and differentiation making individuals incomplete throughout their whole lives, they would be distributed over the different periods of the life of each individual.

As these lines are intended to be an introduction, not a commentary, I will now leave the reader to follow the argument in the book itself.

P. Chalmers Mitchell.

London, August, 1907.

PREFACE

It is now four years since I wrote a volume, the English translation of which was called The Nature of Man, and which was an attempt to frame an optimistic conception of life. Human nature contains many very complex elements, due to its animal ancestry, and amongst these there are some disharmonies to which our misfortunes are due, but also elements which afford the promise of a happier human life.

My views have encountered many objections, and I wish to reply to some of these by developing my arguments. This was my first task in this book, but I have also brought together a series of studies on problems which closely affect my theory.

Although it has been possible to support my conception by new facts, some of which have been established by my fellow-workers, others by myself, there still remain many sides of the subject where it is necessary to fall back on hypotheses. I have accepted such imperfections instead of delaying the publication of my book.

Even at present there are critics who regard me as incapable of sane and logical reasoning. The longer I postpone publication, the longer would I leave the field open to such persons. What I have been saying may serve also as a reply to the remark of one of my critics, that my ideas have been “suggested by self-preoccupation.”

It is, of course, quite natural that a biologist whose attention had been aroused by noticing in his own case the phenomena of precocious old age should turn to study the causes of it. But it is equally plain that such a study could give no hope of resisting the decay of an organism which had already for many years been growing old. If the ideas which have come out of my work bring about some modification in the onset of old age, the advantage can be gained only by those who are still young, and who will be at the pains to follow the new knowledge. This volume, in fact, like my earlier one on the “Nature of Man,” is directed much more to the new generation than to that which has already been subjected to the influence of the factors which produce precocious old age. I think that thus the experience of those who have lived and worked for long can be made of service to others.

As this volume is a sequel to The Nature of Man, I have tried as much as possible to avoid repetition of what was fully explained in the earlier volume.

Here I bring together the results of work that has been done since the publication of The Nature of Man. Some of the chapters relate to subjects upon which I have lectured, or which, in a different form, have been printed before. For instance, the section on the psychic rudiments of man appeared in the Bulletin de l’Institut général psychologique of 1904, the essay on Animal Societies was published in the Revue Philomatique de Bordeaux et du Sud-Ouest of 1904, and in the Revue of J. Finot of the same year, whilst a German translation of it appeared in Prof. Ostwald’s Annalen der Naturphilosophie. The chapter on soured milk first appeared as a pamphlet, published in 1905. The substance of my views on natural death was published in June last in “Harper’s Monthly Magazine” of New York, while the chapter on natural death in animals appeared in the first number of the Revue du Mois for 1906.

I have to thank most sincerely the friends and pupils who have helped me by bringing before me new facts, or other materials; the names of these will appear in their proper places in the volume. I have not mentioned by name, however, Dr. J. Goldschmidt, whose continual encouragement and practical sympathy have made my work much easier.

Finally, my special thanks are due to Drs. Em. Roux and Burnet, and M. Mesnil, who have been so good as to correct my manuscript and the proofs of this volume.

É. M.

Paris, Feb. 7, 1907.

CONTENTS

THE PROLONGATION OF LIFE

PART I

THE INVESTIGATION OF OLD AGE

I

THE PROBLEMS OF SENILITY

Treatment of old people in uncivilised countries—Assassination of old people in civilised countries—Suicide of old people—Public assistance in old age—Centenarians—Mme. Robineau, a lady of 106 years of age—Principal characters of old age—Examples of old mammals—Old birds and tortoises—Hypothesis of senile degeneration in the lower animals

In the “Nature of Man” I laid down the outlines of a theory of the actual changes which take place during the senescence of our body. These ideas, on the one hand, have raised certain difficulties, and, on the other, have led to new investigations. As the study of old age is of great theoretical importance, and naturally is of practical value, I think that it is useful to pursue the subject still further.

Although there exist races which solve the difficulty of old age by the simple means of destroying aged people, the problem in civilised countries is complicated by our more refined feelings and by considerations of a general nature.

In the Melanesian Islands, old people who have become incapable of doing useful work are buried alive.

In times of famine, the natives of Tierra del Fuego kill and eat the old women before they touch their dogs. When they were asked why they did this, they said that dogs could catch seals, whilst old women could not do so.

Civilised races do not act like the Fuegians or other savages; they neither kill nor eat the aged, but none the less life in old age often becomes very sad. As they are incapable of performing any useful function in the family or in the village, the old people are regarded as a heavy burden. Although they cannot be got rid of, their death is awaited with eagerness, and is never thought to come soon enough. The Italians say that old women have seven lives. According to a Bergamask tradition, old women have seven souls, and after that an eighth soul, quite a little one, and after that again half a soul; whilst the Lithuanians complain that the life of an old woman is so tough that it cannot be crushed even in a mill. We may take it as an echo of such popular ideas that murders of old people are extremely common even in the most civilised European countries. I have been astonished in looking through criminal records to see how many cases there are of the murder of old people, specially of old women. It is easy to divine the motives of these acts. A convict of the Island of Saghalien, condemned for the assassination of several old persons, declared naïvely to the prison doctor: “Why pity them? They were already old, and would have died in any case in a few years.”

In the celebrated novel of Dostoiewsky, “Crime and Punishment,” there is a tavern scene where young people discuss all sorts of general topics. In the middle of the conversation a student declares that he would “murder and rob any cursed old woman without the least remorse.” “If the truth were told,” he goes on to say, “this is how I look at the thing. On the one hand a stupid old woman, childish, worthless, ill-tempered, and in bad health; no one would miss her, indeed she is a nuisance to everyone. She does not even herself know any reason why she should live, and perhaps to-morrow death will make a good riddance of her. On the other hand, there are fresh and vigorous young people who are dying in their thousands, in the most senseless way, no one troubling about them, and everywhere the same thing is going on.”

Old people not only run the risk of murder; they very often end their own lives prematurely by suicide.

They prefer death to a life oppressed by material hardships or burdened by diseases. The daily papers give many instances of old people who, tired of suffering, asphyxiate themselves by their charcoal stoves.

The frequency of suicide in the case of the old has been established by numerous statistics, and the new facts which I now cite do no more than confirm it. In 1878, in Prussia, amongst 100,000 individuals there were 154 cases of suicide of men between the ages of 20 and 50, but 295, that is to say, nearly twice as many of men between the ages of 50 and 80. In Denmark, a country in which suicide is notoriously common, a similar proportion exists. Thus, in Copenhagen, in the ten years from 1886 to 1895, there were 394 suicides of men between 50 and 70. These figures relate to 100,000 individuals. Of the suicides 36-1/2 per cent. were those of people in the prime of life, 63-1/2 per cent. those of the aged.1

In such circumstances, it is natural that politicians and philanthropists have made many attempts to ameliorate the old age of the poor. In some countries laws have been passed to bring about this. For instance, a Danish law of June 27th, 1891, established compulsory aid for the aged, enacting that every person more than 60 years old was to have the legal right to aid if required. In 1896 more than 36,000 people (36,246) were pensioned under this law, at a cost of nearly £200,000. In Belgium, the indigent old people are not pensioned until they reach the age of 65. In France, until recently, the aged poor could be supported at the public expense only by prosecuting them and sending them to prison for begging. This state of affairs, however, ceased with the application of the law of July 15th, 1905, according to which any French subject without resources, unable to support himself by work, and either more than 70 years of age, or suffering from some incurable infirmity or disease, is to receive public assistance.

It has been thought the proper course to make such laws, and to lay the burden on the general population, without inquiring if it may not be possible to retard the debility of old age to such an extent that very old people might still be able to earn their livelihood by work. Old age can be studied by the methods of exact science, and there may yet be established some regimen by which health and vigour will be preserved beyond the age where now it is generally necessary to resort to public charity. With this object, a systematic investigation of senescence should be made in institutions for the aged, where there are always a large number of people from 75 to 90 years old, although centenarians are extremely rare. I know many institutions for aged men where, from their first foundation, there has been no case of an inhabitant reaching the age of 100, and even in similar institutions for women, although women live to much greater ages than men, centenarians are very rare. At the Salpêtrière, for instance, where there is always a large number of old women, it is the rarest chance to find a centenarian. Opportunity for the study of the extremely aged is to be found only in private families.

Most of the centenarians whom I have been able to see have been so defective mentally that all that can be studied in them are the physical qualities and functions. A few years ago an old woman who had reached her 100th year was the pride of the Salpêtrière. She was bedridden and extremely feeble physically and mentally. She replied briefly when she was asked questions, but apparently without any idea of what they meant.

Not long ago, a lady who lived in a suburb of Rouen reached her 100th birthday. The local newspapers wrote exaggerated articles about her, praising the integrity of her mind and her physical strength. I paid a visit to her myself, hoping to make a detailed investigation, but I found at once that the journalists had completely misrepresented her condition. Although her physical health was fairly good, her intelligence had degenerated to such an extent that I had to abandon the idea of any serious investigation.

The most interesting of all the centenarians with whom I have become acquainted had reached an extremely advanced age, having entered upon her 107th year. It is about two years ago that a journalist, Monsieur Flamans, took me to see this Mme. Robineau who lived in a suburb of Paris. I found her a very old-looking lady, rather short, thin, with a bent back, and leaning heavily on a cane when she walked. The physical condition (Mme. Robineau was born on January 12th, 1800), of this woman of more than 106 years, showed extreme decay. She had only one tooth; she had to sit down after every few steps, but, once comfortably seated, she could remain in that position for quite a long time. She went to bed early and got up very late. Her features displayed very great age (see Fig. 1), although her skin was not extremely wrinkled.

Fig. 1.—Mme. Robineau, a centenarian. From a photograph taken on her one hundred and fifth birthday.

The skin of her hands had become so transparent that one could see the bones, the blood-vessels, and the tendons. Her senses were very feeble; she could see only with one eye; taste and smell were extremely rudimentary; her hearing was her best means of relation with the external world. None the less, Dr. Löwenberg, a well-known aurist, had assured himself that her auditory organs showed in a most marked degree, the usual signs of old age, such as complete insensibility to high notes and slight deafness for low notes. Dr. Löwenberg attributed these changes to senile degeneration of the ear which affected more and more seriously the nervous mechanism although it had caused little change in the conducting apparatus. Notwithstanding her physical weakness, Mme. Robineau retained her intelligence fully, her mind remained delicate and refined and the goodness of her heart was touching. In contrast with the usual selfishness of old people, Mme. Robineau took a vivid interest in those around her. Her conversation was intelligent, connected, and logical. Examination of the physical functions of this old lady revealed facts of great interest. Dr. Ambard found that the sounds of the heart were normal, but perhaps a little accentuated. The pulse was regular, 70 to 84 a minute, and its tension was normal. The arterial pressure was 17. The lungs were sound. All these facts testify to her general health. The most remarkable circumstance was the absence of sclerosis of the arteries, although such degeneration is usually believed to be a normal character of old age.

Analysis of the urine, made on several occasions, showed that the kidneys were affected with a chronic disease, which, however, was not serious.2

Although the sense of taste was weak, Madame Robineau had a fair appetite. She ate and drank little, but her diet was varied. She took butcher’s meat or chicken extremely seldom, but ate eggs, fish, farinaceous food, vegetables, and stewed fruit, and drank sweetened water with a little white wine, and sometimes, after a meal, a small glass of dessert wine. The processes of alimentary digestion and excretion were normal.

It has sometimes been thought that duration of life is a hereditary property. There was no evidence for this in the present case. Madame Robineau’s relatives had died comparatively early in life, and a centenarian was unknown in her family. Her great age was an acquired character. Her whole life had been extremely regular. She had married a timber merchant, and had lived for many years in a suburb of Paris in comfortable circumstances. Her character was gentle and affectionate; she was thoroughly domesticated, and had been devoted to home life with very few distractions.

At the age of 106 years, her intelligence suddenly became weak. She lost her memory almost completely, and sometimes wandered. But her gentle and affectionate disposition remained unaltered.

The appearance of aged persons is too well known to make detailed description necessary. The skin of the face is dry and wrinkled and generally pale; the hairs on the head and the body are white; the back is bent, and the gait is slow and laborious, whilst the memory is weak. Such are the most familiar traits of old age. Baldness is not a special character; it often begins during youth and naturally is progressive, but if it has not already appeared, it does not come on with old age.

The stature diminishes in old age. As the result of a series of observations, it has been established that a man loses more than an inch (3·166 cm.), and a woman more than an inch and a half (4·3 cm.), between the ages of fifty and eighty-five years. In extreme cases, the loss may be nearly three inches. The weight also becomes less. According to Quételet, males attain their maximum weights at the age of forty, females at that of fifty. From the age of sixty years onwards, the body becomes lighter, the loss at eighty being as much as thirteen pounds.

Such losses of height and weight are signs of the general atrophy of the aged organism. Not merely the soft parts, such as the muscles and viscera, but even the bones lose weight, in the latter case the loss being of the mineral constituents. This process of decalcification makes the skeleton brittle, and is sometimes the cause of fatal accidents.

The loss of muscular tissue is specially great. The volume diminishes, and the substance becomes paler; the fat between the fibres is absorbed, and may disappear completely. Movements are slower, and the muscular force is abated. This progressive degeneration has been examined by dynamometrical measurements of the hand and the trunk, and is greater in males than in females.

The volumes and weights of the visceral organs similarly become smaller, but the diminution is not uniform.

The old age of lower mammals presents characters similar to those found in man. I can now give other instances than the case of the old dog which I described in the “Nature of Man.”

I will first take the case of old elephants, described by a competent observer. “The general appearance is wretched, the skull being often hardly covered with skin; there are deep abrasions under the eyes, and smaller ones on the cheeks, whilst the skin of the forehead is very often deeply fissured or covered with lumps. The eyes are usually dim, and discharge an abnormal quantity of water. The margin of the ears, specially on the lower side, is usually frayed. The skin of the trunk is roughened, hard, and warty, so that the organ has lost much of its flexibility. The skin on the body generally is worn and wrinkled; the legs are thinner than in maturity, the huge mass of muscles being much shrunken, whilst the circumference, especially just above the feet, is considerably reduced. The skin round the toe-nails is roughened and frayed. The tail is scaly and hard, and the tip is often hairless.

Fig. 2.—A Mare, thirty-seven years old.

Fig. 3.—A White Duck, which lived for more than a quarter of a century.

Horses begin to grow old much sooner than elephants. I reproduce (Fig. 2) the photograph of a rare instance of longevity, a mare 37 years old, which belonged to M. Métaine, in the department of Mayenne. The skin, bare in places, but elsewhere covered with long hairs, shows considerable atrophy. The general attitude reveals the feebleness of the whole body. Many birds, on the other hand, show at similar ages very slight external change, as may be seen from the photograph of a duck more than 25 years old (Fig. 3) which belonged to Dr. Jean Charcot. At a still greater age, as may be seen occasionally in parrots, the general debility of the body reveals itself in the attitude, in the condition of the feathers, and in the swelling of the joints. On the other hand, the oldest reptiles which have been observed do not differ in appearance from normal adults of the same species. I have in my possession a male tortoise (Testudo mauritanica) given me by my friends MM. Rabaud and Caullery, and which is at least 86 years old. It shows no sign of old age, and in all respects behaves like any other individual of this species. More than 31 years ago it was wounded by a blow, the traces of which remain visible on the right side of the carapace (Fig. 4). In the last three years the tortoise lived in a garden at Montauban, along with two females which laid fertile eggs. The old male, although, as I have said, probably at least 86 years of age, was still sexually healthy.

Fig. 4.—An Old Land-tortoise.

I have borrowed from the interesting volume of Prof. Sir E. Ray Lankester3 the figure (Fig. 5) and description of a giant tortoise from the island of Mauritius, which is probably the oldest of all living animals. It was brought to Mauritius from the Seychelles in 1764, and has lived since then in the garden of the Governor, and as it has thus already been 140 years in captivity, its age must be at least 150 years, although we have not exact information. Notwithstanding this, it shows no signs of old age.

The examples which I have brought together show that often amongst vertebrates there are some animals the organisms of which withstand the ravages of time much better than that of man. I think it a fair inference that senility, the precocious senescence which is one of the greatest sorrows of humanity, is not so profoundly seated in the constitution of the higher animals as has generally been supposed. It is not necessary, therefore, to discuss at length the general question as to whether senile degeneration is an inevitable event in living organisms.

Fig. 5.—A Water-tortoise, more than 150 years old.
(After Prof. Sir E. Ray Lankester.)

I have already shown, in the “Nature of Man,” the difference which exists between senile degeneration in our own bodies and the phenomena of senescence amongst Infusoria which, as M. Maupas described, are followed by a process of rejuvenescence. According to the more recent results of several investigators, the difference is still greater than I had supposed. Enriquez4 has been able to propagate Infusoria to the 700th generation without any sign of senility being displayed. Here we are far from the condition in the human race.

R. Hertwig,5 one of the best observers of the lower animals, has recently attempted to show that the very simple animalculæ of the genus Actinosphærium are subject to true physiological degeneration. He has several times seen cultures of this Rhizopod degenerate, until all the individuals had died, notwithstanding the presence of abundant food. Prof. Hertwig attributed this to the “constitution of the Actinosphærium having been weakened by too great vital activity at an earlier stage.” I should have thought that it was a much more natural explanation to suppose that the culture had undergone infection by one of the contagious diseases which so often destroy cultures of different kinds of lower animals and plants. As this idea had not occurred to the observer, he had not searched for parasitic microbes amongst the granulations which are always present in the body of an Actinosphærium. However this may be, I cannot accept the facts brought forward by this distinguished German as a valid proof of the existence of senile degeneration in these lowly creatures.

The facts that I have brought together in this chapter justify the conclusion that human beings who reach extreme old age may preserve their mental qualities notwithstanding serious physical decay. Moreover, it is equally plain that the organism of some vertebrates is able to resist the influence of time much longer than is the case with man under present conditions.

II

THEORIES OF CAUSATION OF SENILITY

Hypothesis of the causation of senility—Senility cannot be attributed to the cessation of the power of reproduction of the cells of the body—Growth of the hair and the nails in old age—Inner mechanism of the senescence of the tissues—Notwithstanding the criticisms of M. Marinesco, the neuronophags are true phagocytes—The whitening of hair and the destruction of nerve cells, as arguments against a theory of old age based on the failure of the reproductive powers of the cells

Although it has not been proved that living matter must inevitably undergo senile decrepitude, it is none the less true that man and his nearest allies generally exhibit such degeneration. It is therefore extremely important to recognise the real causes of our senescence. There have been many hypotheses on the subject, but there are comparatively few definite facts known.

Bütschli has supposed that the life of cells is maintained by a specific vital ferment which becomes feebler in proportion to the extent of cellular reproduction, but I cannot regard this as more than a pious opinion. The ferment has never been seen, and we do not know of its actual existence. According to the better-known theory of Prof. Weismann, old age depends on a limitation in the power of cells to reproduce, so that a time comes when the body can no longer replace the wastage of cells which is an inevitable accompaniment of life. As old age appears at different times in different species and different individuals, Weismann has concluded that the possible number of cell generations differs in different cases. He has not found, however, a solution of the problem as to why multiplication of cells should cease in one individual, whereas it proceeds much further in other individuals. Prof. Minot,6 the American zoologist, has developed a similar theory, and has employed an exact method to determine the gradual diminution in the rate of growth of an animal from its birth onwards. According to him, the power of reproduction of the cells weakens progressively during life, until a point is necessarily reached at which the organism, no longer capable of repairing itself, begins to atrophy and degenerate. Dr. Buehler7 has recently laid stress upon this theory.

There is no doubt that cells reproduce much more actively during the embryonic period. The process becomes slower later on, but, none the less, continues to display itself throughout the whole period of life. Buehler attributes the difficulty with which certain wounds heal in the case of old people to the insufficiency of cellular reproduction. He thinks in particular that the proliferation of the cells of the skin, to replace those which are worn off from the surface, becomes less active with age. According to him, it is theoretically obvious that a time must come when the replacement of the epidermic cells completely ceases. As the superficial layers of the skin continue to dry up and be cast off, it is plain that the epidermis must disappear completely. Buehler thinks that there must be a similar fate for the genital glands, the muscles, and all the other organs.

These theoretical considerations, however, are not compatible with certain well-known facts indicating that there is no general cessation of the power of cell reproduction in old age. The hairs and the nails, which are epidermic outgrowths, continue to grow throughout life, their growth being due to the proliferation of their constituent cells. There is no sign of any arrest in the development of these structures, even in the most advanced old age. The reverse is true. It is well known that the hairs on some parts of the body increase in number and in length in old people. In some lower races, for instance in the Mongols, the moustache and the beard grow vigorously in old age, whilst young people of the same race have only very small moustaches and practically no trace of beard. So also in white women the fine and almost invisible down which covers the upper lip, the chin, and the cheeks in the young may become replaced by long hairs which form a moustache or beard.

Dr. Pohl, a specialist in the growth of hair, has measured the rate of growth in different circumstances. He has shown that in an old man of 61 the hair on the temple grew 11 mm. in a month; on the other hand, the hair on the same region in boys of 11 to 15 years old grew in the same time only from 11 to 12 mm. Plainly, there is no case here of a progressive diminution of cell-proliferation with age. The same observer, it is true, has shown that the hair of young men of between 21 and 24 years grew at the rate of 15 mm. a month, whilst in the same individuals, at the age of 61 years, the rate of growth was only 11 mm.; but this diminution in the rate of growth is only apparent. The first figure concerned the hair taken from different regions of the scalp, whilst the second related only to the hair on the temples, and Dr. Pohl himself has shown that, in the latter region, the hair grows slower than in other regions. Moreover, in many boys of 11 to 15 years old, studied by this observer, the rate of growth was always less than 15 mm., and often less even than the 11 mm. recorded in the old man of 61.

I have been able to note that the nails grow even in very old people. In the case of Mme. Robineau, the centenarian, the nail of the middle finger of the left hand grew 2-1/2 mm. in three weeks. In the case of a lady of 32 years old, the corresponding nail grew 3 mm. in two weeks, the difference being out of all proportion to the enormous difference in the age. The centenarian’s nails had to be cut from time to time.

Although the hairs of old people grow, they become white, which is a phenomenon of senile degeneration. Although they increase in length, the colouring matter in them becomes reduced and finally disappears. In the “Nature of Man” I described the process by which this blanching takes place, and which may now be regarded as definitely proved. It is useful as a means of interpreting the real nature of the process of senescence. In several published works, I have explained my belief that just as the pigment of the hair is destroyed by phagocytes, so also the atrophy of other organs of the body, in old age, is very frequently due to the action of devouring cells which I have called macrophags. These are the phagocytes that destroy the higher elements of the body, such as the nervous and muscular cells, and the cells of the liver and kidneys. This part of my theory has encountered very strong criticism, especially with regard to the part played by the macrophags in the senescence of nervous tissue.

Neurologists in particular, have criticised my interpretation. For several years M. Marinesco8