CHAPTER X

INTRODUCTION TO THE SCIENTIFIC STUDY OF OLD AGE

General account of old age—Theory of senile degeneration amongst unicellular organisms—Conjugation amongst infusoria—Old age in birds and anthropoid apes—General characters of senile degeneration—Sclerosis of the organs—Phagocyte theory of senile degeneration—Destruction of higher elements by macrophags—Mechanism of whitening of the hair—Serums acting on cells (cytotoxins)—Sclerosis of the arteries and its causation—Harm done by the microbes of the alimentary canal—Intestinal putrefaction and the modes of preventing it—Attempts to prolong human life—Longevity in biblical times

While I cannot share the views of those who turn from science to seek truth and consolation in religion, it would be wrong to ignore or to be indifferent to the existence of that attitude. There are men who are tormented by the contradiction between the desire of life and the inevitability of death, and when these demand some solution of the problem, it is unreasonable merely to say that they are too exacting and should learn contentment.

If a man complains to his physician of uncontrollable hunger and thirst, he is not told that it is wrong to be so greedy, and that that fault could be mastered by strength of mind. The doctor carefully examines the patient and does what he can for the distressing symptoms, which, indeed, in this case are generally due to diabetes. Those who hunger and thirst after eternal life, ought to be similarly treated by men of science whose duty it is to ameliorate their sufferings as much as possible.

Science has undoubtedly gone far in the successful treatment of disease, both as regards prevention and cure, but it is powerless before those other evils from which Buddha implored his father to grant him exemption—old age and death. Science has attained to heights of knowledge undreamed of by Buddha’s father, King Couddhôdana, and yet it knows no more than he did with regard to the problem of old age and death. Like the king, science can but reply to its questioners: “You ask the impossible. I cannot help you!”

Not only is no remedy for old age known to science, but little or nothing is known with regard to that period in the lives of men and animals. It was no easy task to compress an account of the present position of medicine within a few pages, the subject matter being overwhelming in quantity. With regard to old age it is quite the contrary, our knowledge being so limited that the subject may be dealt with in a few lines. With the advance of years, man and the higher animals undergo important modifications. They become weaker, the body shrinks, the hair whitens, and the teeth decay; in fact, all the phenomena connected with senile decay manifest themselves.

At this period of life which overtakes various species of animals at different ages, the body becomes an easy prey to pernicious influences and diseases. The direct cause of death cannot always be determined, and is attributed to the general breaking up of the system which we call natural death. The first question which presents itself to the scientific mind is whether this degeneration or senile decay is proper only to man and the higher animals, or is common to all forms of life. We have all seen very old trees, the appearance of which proclaims their age. The trunk is decayed, the bark gnarled, the branches shrivelled, and the leaves scanty. Some kinds of trees live for hundreds—possibly thousands—of years, while others age with comparative rapidity. Senile decay is not unknown in the vegetable kingdom, and its presence is suspected even among creatures of very simple organisation belonging to the group of infusoria. These creatures may be reared with ease in vessels containing macerations of chopped hay or leaves. They multiply by means of division (Fig. 12), an operation which takes place at very short intervals, some of them dividing nearly every hour. Owing to this rapid multiplication the vessels soon become full of a mass of infusoria. M. Maupas,[287] a very distinguished zoologist, observed that the infusoria became smaller and smaller after a number of generations, exhausting themselves, as it were, and perishing unless two individuals succeed in uniting. This process of “conjugation” (Fig. 13), involves an exchange of portions of the bodies of the two creatures and brings about a complete rejuvenescence of the two individuals. After conjugation, a process essentially similar to the details of sexual fertilisation, the infusoria resume the normal appearance and again become capable of reproduction by simple division for many generations.

[Illustration:

FIG. 12. Paramecium about to divide in two. ]

The periodical debility, which precedes conjugation is, according to Maupas, an instance of senile degeneration among infusoria. He has recognised its existence in the case of many species of the higher infusoria (_Ciliata_), but while this phenomenon has been observed in the case of many other simple organisms, it cannot be set down as universal among microscopic beings. Among bacteria, a group that includes the greater number of pathogenic organisms, conjugation has been very rarely observed. Even the largest kinds, such as, for instance, the _anthrax_ bacillus, may be propagated for a long series of generations without the occurrence of conjugation.

[Illustration:

FIG. 13. Conjugation of two Paramecia (after Bütschli). ]

Even in the case of the infusoria which by means of the process of conjugation can reproduce indefinitely, the preconjugal debility cannot be identified with the senile degeneration of human beings, the higher animals and trees. In all these debility is the antecedent, not of conjugation and rejuvenescence, but of the end of life.

Another important difference is that in the case of infusoria the preconjugal debility does not occur in every individual, as is the case with the animals and plants which display real old age. In the infusoria an indefinite number of generations occur between the individuals that display debility and those that are ready for conjugation.

If, in spite of these differences, we were to insist on the existence of an essential resemblance between senile degeneration in man and preconjugal debility in infusoria, it would be enough to reflect on the result of applying to the case of man what is an infallible remedy in the case of the infusoria. For conjugation brings about a real rejuvenescence of the infusoria and a similar event in the case of man would only increase the debility. Moreover, according to recent investigations of Calkins,[288] infusoria, weakened by degeneration, may become young again not only by conjugating with their kind, but by the addition of bouillon or extract of brain to the medium in which they live.

Real old age is a phase of existence in which the natural forces abate never to be renewed. In animals, the life cycle of which is very definite, the signs of senile degeneration are not visible. Insects, in the adult condition, very often live only a short time, and die without displaying the slightest mark of age. In the case of lower vertebrates, old age is little known, and has few signs. On the other hand, mammals and birds display senile atrophy in a marked fashion.

Some species of birds live to a great age, longevity being more common than among mammals. Cases in which birds such as geese, swans, ravens, and some birds of prey, have been known to reach the age of fifty years,[289] are not uncommon, whereas such an event is very rare in the case of a mammal. Even small birds, such as canaries, may live as long as twenty years. Parrots are especially long-lived birds. Cockatoos have been known to reach the age of eighty years and more. I myself have had opportunities of observing a South American parakeet (_Chrysotis amazonica_) which lived more than eighty-two years, longer than is usual even with parrakeets. Several years before it died the bird showed unmistakable signs of old age. It became less lively, its plumage, although it did not whiten, lost much of its brightness, and the joints of the claws showed evidence of the presence of disease. In short, the parrakeet was obviously worn out and debilitated.

Mammals show the signs of age even more plainly than do birds. A dog reveals old age by its slow movements, its white hairs, and worn teeth. The appearance of such an animal is never agreeable, while it is often dirty and ill-tempered. Brehm describes the old age of a dog as follows: “At twelve years of age a dog has grown old, and his gait and whole organisation show signs of age. The coat is no longer glossy; the forehead and muzzle are grey, the teeth are blunted or have fallen out. The animal is lazy and apathetic. Many such dogs are dumb and blind. Dogs may live for twenty, six and twenty, or even thirty years, but such cases are most unusual.”

As the dog is a domesticated animal, it might be argued that its old age, with its manifest signs of decrepitude, is the result of the artificial conditions of its life. To decide on this point it is necessary to examine an instance of old age in a wild animal. This presents certain difficulties since wild animals when old and feeble become an easy prey to carnivorous enemies. It will best serve our present purpose to consider such information as has been collected regarding the period of old age in anthropoid apes.

The natives of Borneo have observed “old orangs, which have not only lost their teeth, but being too feeble to climb, live on the fallen fruits and herbs.”[290] Gorillas, according to Savage, turn grey in their old age, from which has arisen the erroneous view that there are two species of the gorilla.

In their wild state, monkeys, like ourselves, are subject in their old age to various distressing ailments. Senile degeneration, then, which is universally looked upon as one of the greatest evils of life, is by no means restricted to the human race. Old age, as portrayed in the Buddhist legend, referred to in chap. vi., is perhaps somewhat exaggerated, but this period of life is undoubtedly characterised by changes of such a nature as considerably to affect the happiness of the old. Buddha, being a pessimist, took too dark a view of this, but let us hear what optimists have to say on the subject. Max Nordau, a doctor, a writer of books and a journalist, says: “Physically speaking, an old man presents an unpleasant picture of decrepitude to the casual observer. Morally speaking, he is a blind and pitiless egotist, having lost all interest in anything outside himself. Intellectually he becomes feeble-minded and narrow in his views, being governed by antiquated notions and prejudices, and incapable of grasping new ideas.”[291]

It may be objected that I am here supporting my argument by quoting from a writer who, in his capacity of clever journalist, rather forces the note. Let me therefore refer to what a learned physiologist said when addressing a serious audience assembled for the purpose of obtaining truth and information from his lips. After dealing in broad outline with the physical degeneracy caused by old age, Longet[292] draws the following mental picture: “The old feel that their task in life is accomplished, and believe themselves to be universally grudged the space they occupy in the world. This renders them suspicious of all around them, and jealous of the young. Their craving for solitude and the uncertainty of their tempers are due to the same cause. All old people are not like this, of course. The hearts of some remain youthful and beat strongly within their feeble frames, but, as a general rule, they are morose and a nuisance to themselves and others, excepting when they are surrounded by their children or grandchildren, who like to listen to them about the past, and who make excuses for the present. Thus the years speed onward, every round of the clock bringing the end nearer, and every hour adding a new wrinkle to their faces, some fresh weakness and some new regret. Their bodies ... become decrepit; their backbones, too weak to hold them upright, curve over and bend them downwards towards the earth.”

There can be no doubt but that the period of old age is sad, and a thorough knowledge of it is necessary before it can be understood. Disease can only be successfully dealt with when the cause of its presence is known, and so it is with old age.

Is it possible, one might ask, at the present stage of the world’s knowledge, to define, with even approximate accuracy, the characteristic features of senile decay? The task is difficult, for although the subject is very important, few facts have been collected.

It is common knowledge that the flesh of old animals, used as food, is tough. An old fowl cannot be compared with a tender and juicy chicken. Organs such as the liver and kidneys are much harder in the case of old animals. The horny flesh of old animals is often compared with boot-leather. Although the comparison does not pretend to be scientific, it is far from being incorrect. Boot-leather is made from the hides of animals; that is to say, of a very resistant material that is called “connective tissue,” and which consists of a dense mass of fibres, mingled with the living elements or “connective tissue” cells. This tissue is very durable and so is employed for boots and shoes.

The infiltration of any organ with connective tissue makes it tough and unpalatable. This hardening is called a _sclerosis_ (of the liver, kidneys, &c.). In old age many organs exhibit this tendency to hardening or sclerotic degeneration. The fact has been known for long, but its significance has been perceived more recently. Demange,[293] in his monograph on the organic changes associated with old age, states as follows: “Besides atrophy and degeneration of the parenchymatous elements,[294] there is to be observed a profound change in the framework of connective tissue, which serves to support the organs. In some cases the skeletal framework of an organ becomes more conspicuous, simply on account of the degeneration of the cells; this is the condition usually present in the liver of aged persons. More often, however, the connective tissue receives some kind of stimulation, which, although it does not amount to inflammation, brings about an active growth and resulting sclerosis. According to the particular case, the hardening occurs in the form of isolated patches or strands, or affects the whole periphery or even the depths of the organ, and smothers the higher elements in its meshes, so producing a further degeneration. The cellular elements disappear gradually, connective tissue taking their place, and the change may be so profound, that as in the case of the prostate gland, the altered organ may actually transcend the normal size, partial or general atrophy, however, being more often the result.”

Sclerosis in old people sometimes takes the form of a hardening of the liver (cirrhosis of the liver) or of the kidneys (renal cirrhosis), but it is the arteries which are most commonly affected by it, producing a symptom of degeneration which is called arterial sclerosis.

Cazalis long ago originated the oft-repeated aphorism: “A man is as old as his arteries,” these vessels, by means of which the blood is distributed throughout the whole system, being of immense importance in the economy of the organism. When the connective tissue is so freely developed as to cause a hardening of the arteries, these are hampered in the exercise of their function and become very brittle. According to Demange, all the special modifications undergone by the body during the period of old age may be attributed to this atrophy of the arteries, but this theory is proved to be an exaggeration by the fact that post mortems on the aged frequently reveal the presence of little or no arterial sclerosis.

It might fairly be supposed that the hardening seen in many organs of the body during the period of old age is universal, and lends greater strength to the frame. The bones, which are separated from one another in youth, become welded together in old age owing to the calcareous deposits in the joints, and the ossification of the joints between the vertebra frequently causes the backbone to assume the appearance of a continuous bone, the greater part of the cartilage having become ossified. In spite of this, and as though for the purpose of proving how physically full of contradictions is the period of old age, the human frame actually becomes lighter and the quantity of component mineral substances becomes less. This brings about a liability to fracture of the bones in old people. The fracture of the neck of the femur is a constant cause of death in the aged, as occurred for instance in the case of Virchow, one of the most distinguished medical scientists of the nineteenth century.

Is science, it may be asked, in a position to state precisely what are the principal modifications which occur in the tissues of old people? At the International Congress of Medicine held at Berlin in 1890, a well-known German anatomist, Merkel,[295] attempted to reply to this question. Speaking of the tissues of old people, he tried to show that certain of these, such as the skin and the mucous membrane (the epithelial tissues), preserve their youthful characters to the end, whereas others, such as the connective tissues, display profound changes. This essay was the first attempt to form a picture of the details of senile degeneration, but it did not reach any simple, general conclusion.

Later on, I myself[296] tried to complete the work, and for the purpose made use of the published results of all the investigators who had studied senile degeneration. I gave a summary of my conclusions in the following words: “In senile atrophy the same condition is always present: _the atrophy of the higher and specific cells of a tissue and their replacement by hypertrophied connective tissue_.” In the brain, the nerve cells disappear; that is to say, the cells which subserve the higher functions such as intellectuality, sensation, control of movement, and these are replaced by elements of a lower kind, in especial by neuroglœa, a kind of connective tissue of the brain. In the liver, the hepatic cells, of great importance to the nutrition of the organism, yield to connective tissue. In the kidneys, that tissue invades and blocks the tubes by which the necessary process of eliminating soluble waste matter is accomplished. In the ovaries, the ova, the specific elements which serve to propagate the race, are similarly eliminated and replaced by granular cells, a variety of connective tissue. In other words, a conflict takes place in old age between the higher elements and the simpler or primitive elements of the organism, and the conflict ends in the victory of the latter. This victory is signalised by a weakening of the intellect, by digestive troubles, and by lack of sufficient oxygen in the blood. The word conflict is not used metaphorically in this case. It is a veritable battle that rages in the innermost recesses of our beings. Distributed throughout every part of our bodies are certain cells which fulfil special functions of their own. They are capable of independent movement, and also of devouring all sorts of solid matter, a capacity which has gained them their name of phagocytes or voracious cells. The function these phagocytes fulfil is a very important one, for it is they that congregate in vast numbers around microbes or other harmful intruders, in order to devour them. Effusions of blood and other elements, on penetrating to parts of the body where their presence is disadvantageous, are absorbed by these phagocytes. In cases of apoplexy, where blood is shed into a part of the brain, setting up paralysis, the phagocytes cluster round the clot and devour the blood corpuscles it has encased. This absorption is a lengthy process, but by degrees, as the pressure of the effusion of blood is removed from the brain, and paralysis disappears, the health of the organism may become completely restored, recovery in such a case being due to the work of the phagocytes. After childbirth, when the uterus presents the appearance of a great open wound clotted with blood, it is again the phagocytes that clean it and re-establish the normal condition. It is plain, therefore, that the part played by these cells is beneficent.

The phagocytes may be divided into small active phagocytes, generally known as the microphags, and larger phagocytes called macrophags, which are sometimes active and sometimes still. The former, which are produced in the marrow of the bones, circulate freely in the blood, and occur as some of the white blood corpuscles, or leucocytes. They are distinguishable by their oval shape which facilitates their easy passage through the smaller blood-vessels, and allows of their accumulating in great numbers in the exudations that form around microbes. These exudations may be formed extremely rapidly, and so may arrest infection in the case of many diseases.

The absorption of extravasations of blood and the healing of wounds are the work of the macrophags. In a general way, the microphags may be said to rid us of microbes, and the macrophags to heal mechanical injuries, such as hæmorrhages, wounds, and so forth. Macrophags possess a single unlobulated nucleus, and occur as white corpuscles in the blood, lymph, and exudations, or as the fixed cells in connective tissues, the spleen, and the lymphatic glands, &c.

[Illustration:

FIG. 14. Section of a Renal Tubule, invaded by Macrophags, from the body of an old man of 90 years. _m_ = macrophag. (From a preparation made by Dr. Weinberg.) ]

[Illustration:

FIG. 15. Cell from the brain of a woman 100 years old being devoured by macrophags. (From a preparation made by Dr. Philippe.) ]

The phagocytes are endowed with a sensitiveness of their own, and by means of a sense of smell or taste are able to recognise the nature of their surroundings. According to the impression made upon this sense, they approach the object which arouses it, exhibit indifference to it, or withdraw from its vicinity. When, however, an infectious microbe finds its way into the body, the microphags are attracted by its excretions and swarm into the exudations surrounding it. The macrophags play a very important part in bringing about senile decay. The atrophy of the kidneys in old persons is attributable to their agency (Fig. 14). They accumulate in large quantities in these organs, clustering round about the renal tubes which they ultimately cause to disappear. Having appropriated the place of the renal tubes, the macrophags proceed to form connective tissue, which thus takes the place of the normal renal tissue. A similar process occurs in the other organs that degenerate in old age. In the brains of old persons and animals, for instance, it is known that a number of nervous cells are surrounded and devoured by macrophags (Fig. 15). Judging from the investigations mentioned above, I think I am justified in asserting that senile decay is mainly due to the destruction of the higher elements of the organism by macrophags. This conclusion has been confirmed by means of direct observation, which was the more necessary as it is contrary to the opinions of some biologists. Marinesco,[297] an authority upon everything connected with the nervous system, has disputed my theory, asserting that the destruction of the specific elements in the nervous centres of old persons is not brought about through the agency of macrophags. In support of his theory, M. Marinesco was good enough to send me a series of preparations from the spinal marrow of persons of very advanced years from which evidence of destruction by means of phagocytes or phagocytosis, was completely absent. I freely admit the absence of phagocytosis in M. Marinesco’s preparations, but these were derived from the cells of spinal marrow, which is much less subject to the ravages of senile decay than is the brain. Even in the lower portions of the encephalon, senility and its parallel, phagocytosis, are uncommon, whereas in the brains of old persons, which are more generally affected by senile decay, the higher elements are clearly shown to undergo destruction by macrophags (Fig. 15). The same phenomenon may be observed in the case of parrots and dogs of advanced age, and in other animals.

So universal a symptom of old age is the invasion of the tissues by macrophags, that it must be regarded as of immense importance. In order, however, to determine more precisely the nature of the function fulfilled by these phagocytes, it was necessary to select a specially favourable subject of investigation. My choice fell upon an examination into the causes of the hair turning white,[298] that being as a rule the first visible sign of approaching old age.

Hair, before it has lost its colour, is full of pigment scattered throughout the two layers of which each hair is composed. At a given moment, the cells of the central cylinder of a hair become active, and proceed to devour all the pigment within their reach. Once they are filled with coloured particles, these cells, which are a variety of macrophag (generally called pigmentophags or more properly speaking chromophags), become migratory, and, quitting the hair, either find their way under the skin or leave the body (Fig. 16). The colouring-matter of the hair is removed in this way by chromophags, leaving the hair colourless.

The process by which hair becomes white is of importance, because it shows that the activity of macrophags is a dominant factor in bringing about senile decay. The brittleness of old people’s bones is probably due to a similar cause, _i.e._, to the absorption and destruction of the framework brought about by macrophags invading the layers of bone. There is still much that remains unknown in this subject, which is well worthy of special research.

[Illustration:

FIG. 16. Hair about to become grey. Chromophags transporting the pigment granules. ]

The activity acquired by macrophags during old age is closely connected with the phenomena that are characteristic of certain chronic complaints. Sclerosis in old persons belongs to the same category as organic sclerosis, which may be set up by various morbid influences. The analogy between senile decay of the kidneys and chronic nephritis, commonly called interstitial nephritis, is incontestable. The destruction of nervous cells through the agency of macrophags, which we have already mentioned as occurring in old age, is equally a symptom of several diseases of the nervous centres, such as general paralysis of the insane. Arterial sclerosis in old persons is actually an inflammatory disease, similar to the inflammation of the arteries set up by other maladies.

The similarity between senility and disease has long been recognised, and partly accounts for the repugnance we all experience at the approach of old age. In childhood and early youth people regard themselves as older than they really are, and long to be “grown-up,” but having once arrived at man’s estate, they do not wish to grow old. An instinctive feeling tells us that there is something abnormal in old age. It cannot be regarded as a part of healthy physiological function. No doubt, because old age is the inevitable lot of mankind, it may be termed normal, in the same fashion as we call the pains of childbirth normal, since few women escape them. In both cases, however, we have to deal with pathological rather than physiological conditions. Just as every effort is made to relieve the sufferings of a woman in labour, so it is natural to try to suppress the evils accompanying old age, but whereas in childbirth an anæsthetic affords relief, old age is a chronic malady, a remedy for which is much harder to find. We have seen that in old age a struggle takes place between the higher elements and the phagocytes, the end being usually a weakening in vitality of the former, while the activity of the latter is enormously increased. It would appear, arguing from this, that one means of fighting against old age, pathologically speaking, would be to strengthen the higher elements of the organism, and to weaken the aggressive capacities of the phagocytes. Let me at once warn the reader that this is not presented as a definite, but as a possible solution of the problem, and is offered for consideration like many other hypotheses on scientific questions. The properties of cellular elements are easily changed when subjected to various influences, and it is therefore not irrational to seek some means of strengthening the blood corpuscles, nerve cells, liver cells, muscular fibres of the heart, and so forth. The task has become easier since the discovery of serums that have specific actions on the tissues.

In the third chapter I stated that serums were known which give precipitates only with the blood of man and of his near relatives the anthropoid apes. Serum of this kind has a definite specific action. Serums may be prepared that dissolve only the red corpuscles of particular species of animals, and that are without action on the other organic elements. It has been found possible, even, to prepare a serum that arrests instantaneously the movements of human spermatozoa, and that is neutral to the similar cells of other animals.

These serums are all prepared in the same way. The cellular elements in question, spermatozoa or red corpuscles, cells of the liver or of the kidney, taken from one animal, are injected into an animal of another species. After several injections have been made, the serum of the animal operated on becomes active with respect to the cells introduced into its body. These serums were discovered by J. Bordet of the Pasteur Institute, but the results have been confirmed by investigators in other countries. The serums are specifically _cytotoxic_, that is to say, they poison particular kinds of cells.

Now it has been shown that such serums, employed in small doses, do not kill or dissolve the specific tissue elements, but actually strengthen them.[299] Here the case is analogous with the action of poisons, such as digitalis, which kill in strong doses, but which in weak doses improve or strengthen the action of certain tissues. In accordance with this indication, experiment has shown that small doses of a serum which is capable of dissolving the red corpuscles of human blood, actually increase the number of those in the body of a patient treated by injections. In the same way, in the case of a serum large doses of which destroy the red corpuscles of a rabbit, small doses increase the number of these elements in the blood.

Here there seems to be a rational method by which we may strive to strengthen the higher elements of the human body, and so prevent them from growing old. The task, at first sight indeed, seems an easy one, only necessitating the injection of a horse (or other animal) with finely minced atoms of human organs, such as brain, heart, liver, kidney, &c., when serums could be drawn off in the course of a few weeks, capable of acting upon those organs. In reality the process would be a very difficult one to carry out, as human organs are rarely obtainable in a condition suitable for injecting into animals. Post mortems can only be legally made twenty-four hours after death, and there are many other obstacles in the way of removing organs from dead bodies. Even if all these difficulties were overcome, another difficulty that would present itself would be the experimenting with various doses of cytotoxic serums of various strength. It is not therefore to be wondered at that the attempt to reinforce the higher elements of the human organism will require much time. If it be necessary to strengthen the higher elements (nervous, hepatic, renal, and cardiac cells), it is plain that they undergo a progressively weakening process. It would be of the highest importance to ascertain the cause of this, for the knowledge would be a guide to future action.

The similarity between senile decay and the diseases entailing atrophy in the more important human organs suggests a similitude in cause. Scleroses of the brain, kidneys, and liver frequently originate in intoxication by poisons such as alcohol, lead, mercury, and so forth, or the disease may be induced by some virus, the virus of syphilis being a common cause.

The immense importance of venereal disease as a malevolent factor in the phenomena of old age, is especially manifested in arterial sclerosis. According to the careful investigations of a Swedish doctor, Edgren,[300] published in his “Monograph on Arterial Sclerosis,” one case in every five of this disease is caused by syphilis, and he shows that chronic alcoholism is an even more frequent cause (25 per cent.). These two factors when united are responsible for nearly half (45 per cent.) the cases of arterial sclerosis that occur. Syphilitic virus and alcohol act as poisons which bring about first degeneration and brittleness of the arterial walls, and eventually a weakening of the higher elements of the organism. The phagocytes, being cells of an inferior order, are less sensitive to these poisons, which accounts for their victory over the poisoned elements.

Rheumatism, gout, and infectious diseases only play a secondary part in setting up arterial sclerosis. Edgren asserts, as the result of very careful calculation, that in nearly every fifth case he found it was impossible to account for the origin of arterial sclerosis. In the majority of cases the sufferers were elderly persons who, according to Edgren, “were afflicted with physiological sclerosis.”[301]

I take it that this sclerosis of unknown origin was by no means physiological but was pathological like that set up by syphilis or alcoholism. The question then arises whence comes the poison in such cases? In syphilis there is a virus of a definite nature to deal with, which causes infection or poisoning, and brings about arterial sclerosis, general paralysis, and other serious ailments. Alcoholism is a poison arising from fermentation, excited by microscopical fungi related to true microbes. Instances of arterial sclerosis which are due neither to syphilis nor to alcohol poisoning nor to any other known cause, can only be accounted for as probably arising from poisoning set up by the mass of microbes congregated in the human intestines. Among these microbes there may be some that are harmless, and possibly even beneficial, but there are undoubtedly a great number the presence of which is extremely prejudicial to health and life. It is impossible to enter into the details of such an important question, and a brief mention must suffice.

The human intestine contains an enormous quantity of bacteria, which, according to the recent investigations of Strassburger,[302] increase at the rate of 128,000,000,000,000 each day. These microbes, of which there are few in the digestive portion of the alimentary canal, are very numerous in the large intestines, _i.e._, in the lower part containing the waste material. The remains of undigested foods and the mucous secretions form a medium very favourable to the growth of microbes. This bacterial flora constitutes a third part of the human excreta. It is very varied, and contains an immense number of different species, among which are bacilli, cocci, and many kinds of other bacteria, about which little is known. The distribution of this bacterial flora shows that it contributes nothing to the well-being of man, being scanty in the digestive portions of the body, and abundant in other parts of the gut. This fact alone suffices to refute the theory of those who attribute great functional importance to the intestinal flora. This theory originated principally from the fact that certain animals perish when brought up under special conditions protecting them from the presence of microbes. Schottelius[303] was the first to try the experiment of rearing chickens in a cage specially constructed for this purpose. The chickens hatched out, and lived for a few weeks: then, there being no microbes within them and only sterilised food being given, instead of increasing in weight, they became thin and showed signs of starvation. Schottelius supplied them with food from which bacteria were no longer excluded, upon which the chickens rallied, and soon became completely restored to health. Madame Metchnikoff[304] tried a similar experiment with tadpoles, which, when kept in vessels and fed upon bread containing the usual microbes, developed normally, but which, when reared under conditions entirely free from the presence of microbes, lived on for some months, but in a degenerate condition, their development being arrested.

On the other hand, Nuttall and Thierfelder[305] succeeded in keeping alive for several days new-born guinea-pigs, the alimentary canals of which were free from microbes, and which were fed only on absolutely sterilised milk and vegetable matter. Notwithstanding this complete absence of microbes the guinea-pigs developed well.

As the two sets of experiments were conducted under conditions arranged so carefully that the chance of error was excluded, it is important to try to reconcile the apparently contradictory results. There is one point common to these three experiments, _i.e._, that they were all executed upon newly born creatures. Now it is well known that at birth the digestive juices are often very imperfectly secreted. In the case of the guinea-pigs, these juices sufficed in quantity for the digestion of the diet provided, whereas in the cases of the chickens and the tadpoles, the digestive juices were incapable of fulfilling their function satisfactorily, and the introduction of microbes endowed with considerable digestive capacity into the intestines compensated for the functional inefficiency of the gastric juices. In addition to the guinea-pigs experimented upon by Nuttall and Thierfelder, there may be mentioned a whole series of lower creatures such as the larvæ of mites and other insects which are able to digest such indigestible material as wax and wool in spite of the total absence of microbes within their intestinal tubes. These experiments are corroborated by the established physiological fact that the gastric and pancreatic juices of mammals easily digest the most varied kinds of foods, even if treated so antiseptically as to ensure the total exclusion of microbes from the intestines.

I need not go further into this subject as the facts which I have cited suffice for my present purpose. The complete atrophy of the large intestines in the case of the woman referred to in chap. iv. proves not only that this portion of the alimentary canal is not indispensable to healthy life, but that life may be maintained in the absence of the flora of the large intestines. And this really is the centre of the problem. The useless bacterial flora may give rise to serious or fatal maladies. Wounds of the abdomen are really serious only when they penetrate the large intestines and so allow the entrance of bacteria from that region to the peritoneal cavity. In such an event, the microbes rapidly multiply in the organism and produce a grave and frequently mortal illness. So long as the microbes remain within the intestines very few of them get into the circulation, and with these few the organism is able to cope. While most of the microbes are confined within the walls of the alimentary canal, the soluble excretions produced by them pass through into the lymph and blood. Quite a number of different facts establish this. Thus, for instance, it has been known for long that the urine of human beings and of animals contains a series of substances such as derivatives of phenol, indol, creosol, skatol, and so forth. In certain diseases the amount of these substances greatly increases. The stagnation of the contents of the intestines increases the amount of phenol and indol. Such facts and many others make it probable that these substances are the products of the bacterial flora of the intestines. They are absorbed by the intestinal wall, pass into the general circulation, and may give rise to various symptoms of a more or less serious nature.

Baumann, who has done much work on the subject, has brought together a series of arguments supporting the bacterial origin of the presence in the urine of the substances in question. Ewald, working from another point of view has obtained strong confirmation of Baumann’s suggestions. He had the opportunity of making observations on a female patient, in whom, on account of a strangulated hernia, an intestinal fistula was established. Throughout the time during which the large intestines were inactive, the urine contained neither phenol nor indol. But as soon as the fistula was closed and communication with the large intestine had been re-established, phenol and indol reappeared in the excreta. Ewald formed the opinion, therefore, that these substances were products of the large intestine.

I need not weary the reader with more of the facts serving to show that the bacterial flora of the large intestines is the source of many poisons harmful to the body. It is among such substances that we must look for the slow poisons which, in the absence of syphilis or alcoholism, produce the arterial sclerosis of old age.

In the fourth chapter I gave reasons to support my view that the large intestine in mammals had been developed because, by storing the products of digestion, it allowed them to run long distances without stopping, and so was an advantage in the struggle for existence. Moreover, the microbes which abound in the contents of the gut make it possible to use certain substances such as cellulose, that are difficult to digest. But these two advantages do not count in the case of the human race. Man does not secure his prey or escape from his enemies by the rapidity of his locomotion. The great development of his intellectual powers has given him advantages of another kind. Moreover, by the use of cooking and the cultivation of plants of high nutritive value, he is able to dispense with the digestion of cellulose.

There is another side to the picture. Ignorant of death and of old age, mammals have acquired the advantages of a large intestine at the expense of longevity. I have already stated that birds live longer than mammals. Birds are practically devoid of a large intestine, and maintain a bacterial flora very much poorer than that found in mammals. There is one exception to this rule, an exception of great importance. Ostriches and their allies, the largest known birds, are characterised by absence of the power of flight and by rapidity of terrestrial locomotion by which they escape their enemies. These are the only birds in which the large intestine is well-developed. The duration of life is much less in their case than in that of smaller birds, such as parrots, ravens, and swans. According to M. Rivière, who has been engaged in ostrich farming in Algeria, these large birds do not live more than thirty-five years. The mode of life, and the shorter duration of life, the huge development of the large intestines and the rich bacterial flora found therein make the ostriches much more like mammals than birds.

It is to be noticed that many birds in which the duration of life is long do not possess a cæcum, the portion of the alimentary canal that contains most bacteria. Examination of the intestinal contents of parrots shows that there exist in these birds very few microbes. A comparative study shows plainly that the existence of an abundant intestinal flora, useless for digestion, helps to shorten life by producing bacterial poisons which weaken the higher elements and strengthen the phagocytes.

The human race has inherited from its ancestors an enormous large intestine and conditions favourable to the life of bacteria. It has to endure the disadvantages of this heritage. On the other hand, the brain of man is very highly developed, and with the increase of intellectual power has come a consciousness of old age and death. Our strong will to live is opposed to the infirmities of age and the shortness of life. Here lies the greatest disharmony of the constitution of man.

If we desired to make the phenomena of old age physiological rather than pathological, it would be necessary to reduce the evils arising from the presence of a large intestine. It is impossible, I may at once say, to wait for the operation of forces independent of the human will and that might lead to the suppression of an organ which has become useless. Man, guided by exact science, must strive to accelerate or anticipate such a result. In spite of the progress of surgery, I do not expect to find in our time that the large intestine will be removed by operation. Perhaps in the distant future such a proceeding will become normal. For the present it is more reasonable to attack the harmful microbes of the large intestine. In the varied flora of that region there exist microbes termed anærobic, because they are able to live in the absence of free oxygen, obtaining what they require by the decomposition of organic matter. Such decomposition is attended by fermentations and putrefactions, and the production of poisons, such as the alkaloids (ptomaines), fatty acids, and even true toxins.

In the human intestines under normal conditions, putrefaction occurs only very slightly, or does not occur at all. But in intestinal diseases of children and of adults, the microbes of putrefaction multiply abundantly and produce copious secretions which inflame the intestinal walls. To avoid these diseases of putrefaction in the case of infants, it has been suggested to use as food only sterilised milk or other foods quite free from microbes. This regimen has proved extremely successful.

In the investigation of the factors that hinder putrefaction, it has been noticed that milk putrefies with considerable difficulty, whereas meat, preserved under the same conditions, decomposes very readily. Investigators have attributed the stability of milk to the presence of casein or of milk-sugar. However, investigations recently made by Bienstock[306] and confirmed by Tissier and Martel[307] have proved the existence of certain microbes that hinder the putrefaction of milk. These are in particular the microbes that sour milk, _i.e._, cause the formation of lactic acid, and which are antagonistic to the microbes of putrefaction. The latter multiply only in an alkaline medium. The lactic acid microbes produce large quantities of acid and so hinder the multiplication of the organisms of putrefaction. Putrefaction takes place rapidly, in spite of the presence of the lactic acid microbes, if there be added soda to macerations of meat or milk. Such facts explain how it is that lactic acid frequently stops some cases of diarrhœa, and why treatment with lactic acid is so useful in maladies associated with putrefaction of the intestinal contents. It makes intelligible, moreover, the medicinal value of fermented milk.

Rovighi,[308] an Italian physician, drank daily a litre and a half of kephir, a preparation made by subjecting milk to lactic acid and alcoholic fermentations. He found that in a few days the products of intestinal putrefaction in his urine either disappeared or were greatly reduced.

It is plain, then, that the slow intoxications that weaken the resistance of the higher elements of the body and that strengthen the phagocytes may be arrested by the use of kephir, or still better of soured milk. The latter differs from kephir in that it contains no alcohol, and alcohol in course of time diminishes the vitality of some important cells in the body. The presence of a number of the lactic acid bacteria is inimical to the growth of the bacteria of putrefaction, and so is of great service to the organism.

But it is not enough merely to introduce useful microbes into the body. We must also prevent the entrance of “wild” microbes, many of which are harmful. Soil, especially when it has been manured, contains large numbers of microbes, some of which are harmful. Bienstock found that the soil of the strawberry-beds in his garden contained the bacilli of tetanus. For three weeks he swallowed some of this soil, but found that the bacteria were destroyed in his intestines, which he attributed to the action of the normal bacterial inhabitants of the alimentary canal. It is probable that if this arresting action were weakened the body would be infected by tetanus from spores of the tetanus microbe swallowed with earth or strawberries or green vegetables. Moreover, besides the organisms of tetanus, there are many other dangerous anærobic bacteria in manured garden soil.

Obviously we should eat no raw food, but confine our diet rigidly to food that has been thoroughly cooked or sterilised. The exclusion of “wild” microbes and the introduction of beneficial microbes, such as those of lactic acid fermentation, must be of great service to health. I know of individuals who have derived great benefit from such a regimen.

Science, even in its present imperfect condition, has many weapons by which to prevent or at least diminish the slow and chronic poisoning of the organism that leads eventually to the degeneration of the higher elements. When these elements are being destroyed by syphilis or alcoholism the struggle must be directed against these evils. It is long since we have known how to do this; that success has not been greater is due to the carelessness of the people who are concerned.

To strengthen the resistance of the higher elements and to transform the “wild” population of the intestine into a cultured population, these are the means by which the pathological symptoms may be removed from old age, and by which, in all probability, the duration of the life of man may be considerably increased.

If it be found impossible to eliminate all the harmful microbes from the flora of the intestines, those that are refractory may be rendered harmless by appropriate serums. We know already a serum that is specific against the microbe of botulism, an organism capable of exciting serious disturbance if it gain entrance to the alimentary canal.

Our inmost convictions assure us that life is too short, and since the remotest ages attempts have been made to prolong it. I need hardly mention the quest of the Middle Ages for an elixir of life, but many thoughtful men have occupied themselves with the problem.

Descartes, who was deeply interested in the subject, believed himself to have found a mode of lengthening human life. Bacon published a tract on life and death, and in it gave advice as to how old age might be reached; blood-letting and the use of saltpetre were parts of his specific.

One of the oldest methods in the world consisted in bringing old men in contact with the bodies of young girls. David, King of Israel, employed this method, which at a much later period came into fashion.

Eighteenth-century quacks proclaimed a number of specifics, among which was the “holy water” of Saint Germain, an infusion of senna, merely purgative in its effects. It is certain that some of the medicines used for the purpose, by emptying the large intestine, decreased the bacterial flora, and so checked the formation of the poisons that are harmful to the higher elements.

Hufeland,[309] a well-known German professor, published towards the end of the eighteenth century, a work called “La Macrobiotique”; or, “the Art of Prolonging Human Life.” This treatise had a great vogue in its day, and contained many interesting and just observations. Besides advocating cleanliness and moderation, Hufeland advised that “we should use vegetable rather than animal food, as animal food was more liable to putrefaction, whilst vegetable substances contained an acid principle that retarded our mortal enemy, putrefaction.”[310] Here the physician of a day long past anticipated one of the discoveries of modern science.

In our time scientific men have not ceased to concern themselves with the prolongation of human life. Professor Pflüger, of Bonn, one of the most distinguished of living physiologists, has published an essay[311] in which he gave the results of his inquiries into this subject. He first stated that investigations into the habits of those who had attained a great age did not give information sufficiently exact. Pflüger laid stress on the means of avoiding infectious maladies, and summed up as follows: “Finally, I can do no better than to associate myself with the advice given in all the treatises on the prolonging of life: avoid the things that are harmful and be moderate in all things.”

A year later, a well-known German physician, Dr. Ebstein[312] published a very careful treatise on the same subject. He had been struck by the fact that among those who have reached a great age, there have been several who had led an exuberant life, full of excesses, notably in the consumption of alcohol. None the less, Ebstein advised either a complete avoidance of alcoholic liquor, or at the most an extreme temperance in the use of it. He prescribed in addition the simplification of the conduct of life and the avoiding of anything that is unwholesome.

Study of such works, which are written in a scientific spirit, convinces me that a science of the prolongation of life could be built up. An exact investigation of the phenomena of old age would contribute to this object. At any rate, we cannot set aside as chimerical plans to make old age a natural process, and one easy to bear. I believe, moreover, that attempts to prolong life deserve to be encouraged, the more so as instances of longevity are already numerous.

Quite a number of cases of centenarians who have preserved intellect and vigour until death have been recorded. It is unnecessary to relate the histories of these persons, of whom some attained such ages as 120, 140, and even 185 years (Saint Mungo of Glasgow). My friend, Professor Ray Lankester,[313] thinks that such unusually old persons are monstrosities comparable with those who have attained a gigantic stature. But centenarians are more numerous than giants, and while the latter exhibit marked signs of pathological weakness the former surprise us by their health and vigour.

The longevity of the Israelites recorded in the Old Testament is well known. No doubt there is much exaggeration in these naïve records. Was it an error of exaggeration to impute an age of 969 years to Methusaleh, or of 595 to Noah, or were these ages reckoned on a different basis? Henseler[314] suggested that in these cases each season was counted as a year, so that the age of Methusaleh was really only 242 years, a length of life not so vastly greater than ages recorded in modern times.

There is evidence to show that in somewhat later Biblical times ages were reckoned in our years. Thus in the Book of Numbers (i. 3, 20, 22) reference is made to those “From twenty years old and upward, all that are able to go forth to war in Israel.” The limit of age given shows clearly that the years counted were our years. This interpretation is supported by many other passages in the Pentateuch, notably where annual harvest feasts are spoken of. We may therefore accept as probable the assignment of such ages as 100 or 120 years to several Biblical personages, such as Aaron, Moses, and Joshua. And the words put in the mouth of Jahveh may be accepted as important evidence: “And the Lord said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.”[315]

The longevity of that remote period must have surpassed the age of the present time. From the circumstance that the greatest number of deaths occurs at the age of seventy years, Ebstein[316] has inferred that seventy years is the normal duration of life. Although there is no doubt but that the duration of human life has become longer in the nineteenth century, we must believe that it was still longer in Biblical times, a fact that is not particularly surprising.

I have called attention to the important influence of syphilis in inducing premature and pathological old age, as that disease is a chief cause of arterial sclerosis and degeneration of the higher elements of the body. Syphilis has an influence still more serious because its effects are inherited. Now although the Bible refers to diseases of the genital organs and lays stress on circumcision, there is no direct evidence in it as to the existence of syphilis. Ebstein, in a treatise on the medicine of the Bible,[317] is confident that there is no reference to syphilis in that Book. Moreover, in the ancient world generally, syphilis was either unknown or existed only in an attenuated form. Haeser,[318] the author of the best modern treatise on the history of medicine, thinks that if syphilis did exist in the ancient world, it occurred in a localised form and did not become a general disease of the system as is the case among the moderns.

Humanity would make a great stride towards longevity could it put an end to syphilis, which is the cause of one fifth of the cases of arterial sclerosis. The suppression of alcoholism, the second great factor in the production of senile degeneration of the arteries, will produce a still more marked extension of the term of life. Scientific study of old age and of the means of modifying its pathological character will make life longer and happier. Although modern knowledge is still imperfect, there is no reason to be pessimistic on the subject of old age.