II.

Notwithstanding the strange powers of protoplasm, and notwithstanding that these are accumulated and intensified in the body, as we saw in the last chapter, there are immovable limitations to vital activity.

This is a fact familiar to all. We can trace diminishing vitality through a series of stages, from slight fatigue right up to death itself. Sleep is perhaps one of the most interesting, though it is little understood. During sleep and the hypnotic trance, we know that the cells of the hemispheres pause in their work and chemically recruit themselves; that there is an interruption of consciousness; and that changes occur in the respiratory and circulatory, and, in fact, in most of the functions. But exactly how these states are induced we do not know. It has been suggested that during sleep less blood passes through the brain; but this is unlikely, and still less probable is it that the nerve cells draw in their processes and shut up like sea-anemones, as another daring theorist supposed. We can only draw parallels between the cells of the central nervous system and any others; all need rest.

The simplest unicellular animals, which we have mentioned so often already, spend their lives in alternate spells of activity and rest. In the third essay we mentioned briefly the weakening of each successive response when a muscle, in which tissue fatigue has chiefly been studied, is stimulated. Before the muscle contracted it contained a form of sugar; when it is tired the sugar is gone, and has been replaced by the products of the chemical action by which the energy was evolved. A period of rest must then follow, for the muscle to be cleansed and replenished. The case of glands, described in Essay II., is somewhat similar. After the gland cell has discharged its ferment, it must spend some time secreting a fresh stock before it is ready to discharge again. In fact, a cell seems to load itself up with supplies, like a locomotive with coal, and, after working till the fuel is nearly exhausted, it has to stop to take in more.

All the cells in the body rest at times; even the cells of the heart, carefully as they are nourished and incessant as their work seems, rest between each beat, and the cells of the nervous system form no exception. The brain no less than the body requires periodic rests to renew its chemical stores, and these rests have to be all the longer, as during the waking hours the brain works harder and less intermittently than any other organ. It is only because the brain is the seat of consciousness and the source of voluntary movements that these phenomena are suspended during sleep.

Death may seem at first sight a very simple affair, the breaking up of protoplasm into simpler non-living compounds; but the death of the body is anything but simple—in fact, it is not always easy to say when the body is dead. Usually, however, it is considered dead when the central nervous system has succumbed, though the muscles may continue to live for several hours.

Death may begin in many ways. The loss of some organs will bring death only after a considerable time, while the failure of others disturbs its economy fatally, and causes an almost immediate cessation of the vital functions. Any interference with the normal conditions of the brain, heart, or lungs is very dangerous, and it is injury or disease of one of the three which puts an end to most men’s troubles. If the brain weakens so that it no longer keeps the heart beating or the muscles, which fill and empty the lungs, to their duties, the body, for obvious reasons, can no longer keep up the cycle of changes we call life. On the other hand, if the lungs cannot oxidize the blood, or the heart drive fresh pabulum to the brain, that organ collapses immediately, and, if a stream of pure blood is not quickly restored to it, dies. No return of the circulation can then restore it; the death of the rest of the animal must follow.

Being the most delicate, the cells of the central nervous system usually die first, and we then say that the man is dead. So the body may be, but much of the protoplasm of which it is composed—whole organs, in fact—remains alive; the muscles will respond to electrical stimulation, and in case some people may dispute that this is a sign of life, if pieces of his skin be removed and grafted into another person, they will grow there, produce hair, and become, in fact, a part of the new body. This they could not possibly do if they were dead; we cannot endow inanimate matter with life.

As death creeps on over the tissues, the leucocytes die, and in doing so form a ferment which solidifies one of the proteids dissolved in the blood, so that the familiar clotting takes place. By a similar process certain constituents of the muscles are also clotted, the muscles stiffening and passing into what is technically, but also pretty generally, known as rigor mortis. Rigor is said to set in soon after death if the body is kept in a warm place, or if death has been preceded by violent exercise; but death in this instance means only the death of the body. It is at the precise moment that a muscle fibre dies that it passes into rigor. By keeping it cool, so that the processes of life may go on slowly, especially if it be in a healthy condition, its death may be deferred for hours; while, on the other hand, at the end of a severe and protracted battle, exhausted soldiers sometimes die instantaneously on being shot, and are found fixed in the position in which the fatal bullet found them—on their knees, with gun to shoulder, in the act of firing.

But if the manner of death is not to be lightly dealt with, its causes are still more obscure. It seems natural enough that people should be killed by violence or by diseases with an external or septic origin, or even by one particular organ wearing out and involving the whole body in the fate of its part. But why should people die of old age? Why should their vitality ebb till they quietly go out? Life is a mechanical cycle of changes. For a time even after it has stopped growing, the body replaces what it wastes, and keeps itself in a condition of equilibrium. Why, then, without any apparent external cause, does it, after a more or less circumscribed period, enter into a decline? And, finally, could we, by taking the proper precautions, delay or prevent old age and death?

In the first place, regarding protoplasm as a chemical structure, why, if kept under favourable conditions, should it ever break down? We have no reason to suppose that it need. It is hard to see how the minute animals, consisting of only one cell, can die of old age, provided that no injurious influence be brought to bear upon them. When an individual has grown to a certain size, it divides in two, and each enters upon life afresh. Why, therefore, should not all the cells of the body continue to renew their youth?

The reason why the body can only last a certain time, in spite of the many quacks with recipes for immortality—recipes including such items as the avoidance of all trouble, worry, or work—must remain a secret until we know the chemical basis of life. It seems to lie in the cell. If a unicellular organism, as described above, be placed in a vessel of sterilized water and left to live alone under otherwise ideal conditions, it will start dividing and multiplying, as though it meant to reproduce itself indefinitely. After a time, however, the shoal begins to deteriorate; each successive generation is feebler than the last, and eventually all die. If, however, before this happens one of the effete cells be placed in another vessel with a similar individual derived from a different ancestor, the two will fuse and form a single fresh animal with entirely restored vigour, ready to multiply to the same extent as either of its original ancestors. A few individuals of a different stock will in this way revivify the whole brood.

There is, therefore, evidently something in the cell which wears out after it has divided a certain number of times—something which must be restored by blending with cells of another strain. What this is we do not know, and perhaps never shall. The most we know is that it seems to be something inherent in the nucleus, not the main body of protoplasm of the cell, for some unicellular animals do not fuse, under the circumstances related above, but exchange only pieces of their nuclei, and yet derive the advantages of mutually increased vitality. But if we apply the fact to our conception of the body as a vast colony of cells with a common origin, we find that it has an important bearing upon the duration of its life.

The single eggcell which gave rise to our schematic embryo in Diagram 3, Fig. 1, was formed by the fusion of two cells shed by two distinct animals. How this one cell grows and multiplies by division is roughly shown in the diagram and those immediately following it; but though the cells do not separate, but hang together and form a body, it is obvious that the colony only amounts to a shoal of unicellular organisms, like that described above as growing weaker with each successive division unless blended with individuals of a different stock. This cannot be done in the body; what would become of our individuality even if such a thing were possible? The body can help to give rise to new bodies, but its own tissues must wear out, and when the colony of cells is exhausted it must die. Careful diet and regular habits, the minimum of wear and tear, may enable the body to run its full term; but they cannot lengthen the lease of life.

So far only can the physiologist take us. Physiology may teach us how to develop our powers and economize our strength; it is already beginning to convert medicine from an art into a science; it will, it is to be hoped, shortly work a revolution in our at present barbarous ideas of how to rear and educate children; it may, in short, teach us how to make the very most of life and die easily; but not until, if ever, it understands the physical basis of life, and perhaps not even then, will it be likely to succeed in prolonging a man’s days much beyond the traditional fourscore years.

CONCLUSION.

While the physiologist is quietly working, making slow but sure progress, his critics, friendly and otherwise, buzz about him like bees. There are some who are in a chronic state of excitement, expecting a revolutionizing discovery from hour to hour; there are others who assure him that he has reached the limit of human powers of comprehension, and can never know much more than he does to-day; and, lastly, there are those who declare that he has done next to nothing, and that his utmost endeavours have failed to effect any real result, and leave all the important secrets of life untouched.

No one knows better than the physiologist how mistaken is the oversanguine class first mentioned. In no department of science, certainly not in physiology, is it possible to reach the top of the ladder by a bound; each rung must be mastered in order. In invading the unknown land the scientist must thoroughly explore and effectively occupy as he advances. He must annex as he goes along; the flying columns which try to reach the enemy’s capital by a dash are never heard of again. In physiology the publication of the various steps is sometimes withheld until the objective has been reached, but our knowledge of life is like Solomon’s temple: a David collects the material, and his successor raises the edifice. The world watches it grow. It is not like those bewildering and unstable palaces of the ‘Arabian Nights,’ built by genii in a single night, and often vanishing as mysteriously.

In every age there have existed people who declare that men can never know more than they do at the moment. There were plenty of them when the science of physiology was unborn, and there will be plenty more of them a hundred years hence; only then they will refer with tolerant amusement to the crude and elementary ideas of their predecessors at the beginning of the twentieth century.

The third class, who take such delight in minimizing the achievements of the physiologist, usually are found, if anyone takes them seriously, to know very little either about the science of physiology itself or the history of its growth. I leave the reader to form his own verdict upon the value of the results obtained from their exceedingly brief and sketchy description in this little volume, with the remark that the science is barely more than three-quarters of a century old, and the most important additions to our knowledge have been made within the last twenty years.

There were, paradoxical as it may sound, great physiologists before then; the work of Harvey, who three centuries ago discovered the circulation of the blood, is above all praise; but how nebulous must have been their ideas may be seen from the following facts: It was only at the beginning of the nineteenth century that the atomic theory of matter was formulated; it was not until twenty years later that the world was startled by a daring chemist who showed that organic compounds obeyed the same natural laws as inorganic; and not until ten years later was the cellular structure of animals, the groundwork in all study of life, recognised.

Even when the science was set upon firm foundations, progress was at first necessarily slow: the organic chemist took some time in examining and classifying the compounds met with in the body—he has not finished yet; and even when the cell theory was grasped, it required much ingenuity and long patience to devise ways of examining organs under the microscope, so that their structure could be made out. The microscope itself was a poor toy fifty years ago, magnifying a diameter ten times where now it magnifies a hundred, and giving only a dim and distorted image. The perfecting of the microscope, and the introduction of anæsthetics and antiseptics, have led to enormous strides being made within the last two decades.

The result of the advance in chemical knowledge, and the introduction of fresh aids to investigation, led to the discarding of vital force as a working hypothesis. Vital force was the bane of the earlier biologists. They made it accountable for all they could not understand, and with this restatement of their difficulties—a restatement which they called an explanation—refrained from further research. But when it was found that many of these inexplicable phenomena, though refractory, yielded to careful study, and could be explained by chemical and physical laws, the physiologist ceased to say of them, ‘They are problems connected with Life, and therefore explained by Vital Force, which is past man’s understanding,’ and frankly admitted that there were many things which he did not as yet fathom. Recently a vitalistic school has cropped up again, declaring that all that it cannot understand must infallibly be due to some occult agency. It shows remarkable vitality in surviving the shocks of successive discoveries.

Turning once more to the present day, we will conclude with a brief glance round a physiological laboratory, and see by what methods the physiologist is preparing future surprises. The chemical department first claims our attention. The imports and exports of animals are carefully balanced, and the changes produced in the food examined. The animal is enclosed in an airtight chamber, air of known composition being pumped into it, and the air which escapes analyzed. The animal most used for this experiment is man himself, since he will take rest and exercise to order, the latter usually on the treadmill, by which it can be also measured, and can be relied upon not to while away the tedium of his imprisonment by gnawing holes in the walls or upsetting his food.

All the substances used as food, found in or excreted by the body, are being thoroughly studied; but it should be remembered that this is chemistry, not physiology. Physiology is only concerned with protoplasm, and the physiologist who goes deeply into the chemistry of non-living matter has to discipline his mind against forgetting its ceaseless change, and trying to regard it as though it were constant. The actual chemistry of protoplasm will be a very hard nut to crack, and may defy us until we can depict molecules as well actually as we now can symbolically. Some idea of the difficulty may be formed if we consider that it is impossible to imagine a pure sample. From the restless activity which is the condition of its existence, it is always working changes in its surrounding, always mixed with raw material, and always masked by the products of its own metabolism. Even if we withhold the former, it consumes its own substance until the moment of death. It does not even look homogeneous under the microscope.

Before, however, we can pursue the chemical methods further, it will be necessary to describe the histological. The reader may have already wondered how we managed to find out so much about the cellular structure of the body. It is no easy matter to cut up soft tissue, of the consistency of an unboiled egg, into thin slices which can be examined under the microscope. It is done in the following manner: The bloodvessels of the freshly killed body are injected with a fluid which instantaneously kills and fixes the cells in much the same way as an egg is fixed by being hard-boiled. The natural shape of the cells is thus preserved, and the loss of any of their chemical constituents by putrefaction prevented. The piece of organ is then impregnated with and cast in the middle of a solid block of paraffin wax, which is put into a machine and shaved up into thin slices, about 40,000 to the inch sometimes. One of these shavings is then stuck upon a glass slide, and on the wax being dissolved away with some such substance as benzine, a section of the tissue, about one cell thick, is left on the glass ready for microscopic survey.

To do anything like justice to the histological methods would require a volume in itself. When the sections are fixed upon slides, they are treated with a number of reagents to show their chemical and structural peculiarities. One section is stained specially to show the nucleus; another to show the centrosome; another zymogen granules, etc. And, as all these cannot be shown at their best in one cell, the differently treated sections have to be separately drawn or photographed, and the typical structure compiled from several. By careful staining, the chemical composition of the different parts of the cell is being worked out, and the effects of rest, activity, feeding, and other influences, studied.

Take as an example the effects of a meal. A number of animals of the same litter are fed together out of the same trough. One has been killed before the meal, and the rest are killed at intervals dividing the time which must intervene before their next feeding-time comes round. Series of sections from their organs are prepared, one from each animal being mounted in order upon the same piece of glass, dipped in the same reagents, and examined under the same microscope. From a number of these sections the progressive effects of a meal upon each of the several constituents of the cell are traced out, and some of the chemical processes deduced.

Turning to the physical side of physiology, it is unnecessary here to say more about the means employed for studying the properties of muscle and nerve than that many of the phenomena occur with such extreme rapidity that they can only be perceived by the photographic plate. In the study of the large organs, the physiologist finds a fascinating employment in devising models in which, so far as possible, all the physical conditions are reproduced, and this not only for the benefit of his pupils, but to help himself in perceiving their meaning. Too much reliance must not be placed on these models, of course, but they have added considerably to our knowledge of the eye and throat.

It requires no great imagination to perceive the difficulties which lie in the way of studying the nervous system. Tracing nerve fibres under the microscope through interminable series of sections is a labour which can neither be hurried nor scamped. It is greatly aided by pathological specimens. An animal which has been through life with only one eye will obviously have central organs of vision showing wide contrasts. Those connected with the blind eye will be undeveloped, because never used, while the corresponding lobes of the brain connected with the other eye will show the effects of doing extra work.

Many of the problems which meet the physiologist can only be solved by experimenting upon a live animal, and these experiments form by no means the easiest part of his work. The animal must be kept, so far as possible, under physiological conditions—that is to say, free from pain and fright and unpoisoned by drugs. Thanks, however, to an extensive knowledge and skilful use of anæsthetics, the obstacles to this method of investigation have been overcome, and its results have proved very profitable. The absence of pain is a very important factor in an experiment, and even if the physiologist took the wanton delight in inflicting suffering which the imagination of his enemies attributes to him, he would have to restrain its indulgence in his laboratory, or forego the hope of even moderate success. In this country, moreover, the Government will not allow such experiments without its express permission, and the license is very rightly only granted to men whose researches promise an adequate return, and who are likely to conduct them humanely and successfully.

Physiological research is not a hobby to be lightly taken up. It is not one merry round of exciting tussles with tortured and infuriated cats and dogs; on the contrary, it entails arduous labour and needs infinite patience. The experiments, often tedious in themselves, have to be repeated again and again in as many different ways as possible, until every slight difference in result can be accounted for; and the certainty that both the methods used and the interpretation given will, when published, receive the closest, and not in every case the friendliest, scrutiny by other members of the profession serves as an admirable corrective to jumping at conclusions. It is, however, an occupation of absorbing interest, and the physiologist feels amply repaid if he can think that his labours have added, no matter how little, to that control over Nature which the severe conditions of modern life make every day more pressingly necessary.

INDEX

A.

Abdominal circulation, 54

Absorption, 25

Acid, hydrochloric, 23

Afferent system of nerves, 92

Alcohol, 95

Alimentary canal, length of, 19 movements of, 46 origin of, 17 structure of, 46

Amœba, 16

Amœboid movement, 31

Amount of food, 15, 96

Animalcula (unicellular micro-organisms), 5, 8, 16, 31, 102, 105

Aorta, 51

Arm, 57

Artery, 48

Association centres, 91

Athletes, 98

Atom, 2

Auditory mechanism, 74

Auricles, 49

B.

Bacteria, 23, 44

Beaumont, 25

Bile, 24, 62

Blind, experiments with the, 100

Blood, 26 circulation of the, 48 clotting after death, 104 corpuscles, 29, 45 course of the, 27, 55 pressure, 51, 66

Body, the, 9, 94

Boils, 45

Bone, 36, 56, 98

Brain, 63, 79, 102

Breathing, 25, 52, 82, 97