Physiological Idea Of Life
( Originally Published 1909 )
ACCEPTING the complicated processes of metabolism and reproduction as distinguishing characteristics of life, the force back of these distinctive powers or properties of living matter becomes a fruitful topic for investigation. Thompson in the `Science of Life' discusses this question. "Over and over again in the history of Biology the doctrine of a special vital, force has arisen, held sway for a time, and then disappeared. It arises as a reaction from the false simplicity of premature solutions, or as a despairing retreat in the face of baffling problems, or as the result of misunderstanding the real aim of science.
"The doctrine is an old one, for even if we ignore the speculations of the ancients, it must date at least from Paracelsus and Van Helmont. As it has naturally taken very different forms in different generations, the word `vitalism,' so often used, has little definite meaning. There is a sense in which no modern physiologist is a vitalist, since none rejects physico-chemical interpretations as the early French vitalists did; there is a sense in which all modern physiologists are vitalists, since none pretends to know the secret of that particular synthesis which even the simplest of organisms illustrates.
"The phrase 'vital force' may be used as a general expression for the energies resident in living matter, and may serve to suggest that we do not at present understand them, or how they are related in the unity of the organism.
But the phrase was originally used to denote a 'hyper-mechanical force,' a mystical power, resident in living creatures, and quite different from thermic, electric, and other forms of energy. This was the meaning attached to the phrase by the disciples of Haller, by Louis Dumas (1765-1813), by Reil (1759-1813), and the other early vitalists. It can only be said that an appeal to such a force violates the scientific method, and abandons the scientific problem. Again and again, in regard to particular points, subsequent progress has shown that the loss of faith in science was premature.
"According to the hypothesis of vitalism the phenomena of life are inexplicable apart from a special vital force exclusively resident in organisms, and different from the chemico-physical energies of the inanimate world. Thus the great pathologist and anatomist Henle (d. 1885) believed in a non-material agent associated with the organism, 'presiding over the metabolism of the body, capable of reproducing the typical form, and of endless partition without diminution of intensity.' It is altogether an error to suppose that a refusal to believe in such a special 'vital force' implies materialism. The questions are quite separate; the former has to do with scientific method, the latter is a philosophical theory. Thus Huxley was certainly no believer in 'a vital force,' yet he was clearly an idealist ; and the same might be said of many.
"Every physiologist will, I believe, admit that he cannot at present give a physico-chemical interpretation of con-tractility or of irritability, of digestion or of absorption, of respiration or of circulation. What he can give is a partial analysis of these functions in simpler terms. This must remain the case until we discover the secret of the synthesis which the simplest unicellular organism expresses. The 'neo-vitalists,' such as Bunge and Rindfleisch, emphasize the fact that there is no present possibility of giving a complete chemico-physical restatement of any observed function; that there are always residual phenomena; and that the known physico-chemical causes do not seem adequate to the result. In other words, the categories of mechanism, of chemistry and physics, cannot be forced upon vitality without doing violence to the very idea of the organism a complex adaptive synthesis of matter and energy whose secret remains unread. When the neovitalists go further, and insist on an idealistic as opposed to a materialistic conception, they may be quite correct, but they are raising another question, which is philosophical rather than biological."
Huxley, in his famous address 'On the Physical Basis of Life,' has well stated the case against the existence of a vital force. "What justification is there, then," he says, "for the assumption of the existence in the living matter of a something which has no representative, or correlative, in the not living matter which gave rise to it? What better philosophical status has 'vitality' than 'aquosity'? And why should 'vitality' hope for a better fate than the other 'itys' which have disappeared since Martinus Scriblerus accounted for the operation of the meat jack by its inherent 'meat roasting quality,' and scorned the 'materialism' of those who explained the turning of the spit by a certain mechanism worked by the draft of the chimney?
"If scientific language is to possess a definite and constant signification whenever it is employed, it seems to me that we are logically bound to apply to the protoplasm, or physical basis of life, the same conceptions as those which are held to be legitimate elsewhere. If the phenomena exhibited by water are its properties, so. are those presented by protoplasm, living or dead, its properties. If the properties of water may be properly said to result from the nature and disposition of its component molecules, I can find no intelligible ground for refusing to say that the properties of protoplasm result from the nature and disposition of its molecules."
This idea of the physical basis of life, so clearly stated by Huxley, has been further developed by Dr. Michael Foster, whose line of thought is as follows : "The more the molecular problems of physiology are studied, the stronger becomes the conviction that the consideration of what we call structure and composition must, in harmony with the modern teachings of physics, be approached under the dominant conception of modes of motion. The physicists have been led to consider the qualities of things as expressions of internal movements; even more imperative does it seem to us that the biologist should regard the qualities of living matter (including structure and composition) as in like manner the expressions of internal movements. He may speak of living matter as a complex substance, but he must strive to realize that what he means by that is a complex whirl, an intricate dance, of which what he calls chemical composition, histological structure and gross configuration are, so to speak, the figures; to him the renewal of protoplasm is but the continuance of the dance, its functions and actions the transferences of the figures. It seems to us necessary, for a satisfactory study-of the problems, to keep clearly before the mind the conception that the phenomena in question are the result, not of properties of kinds of matter, but of kinds of motion."
Before passing from the consideration of vital force and the physical basis of life, it will be of interest to compare the views of the biologists Huxley and Foster with that expressed in a lecture by the great physicist, Tyndall.
"The origin, growth and energies of living things," he reminded his hearers, "are subjects which have always engaged the attention of thinking men. To account for them it was usual to assume a special agent, free to a great extent from the limitations observed among the powers of inorganic nature. This agent was called vital force; and, under its influence, plants and animals were supposed to collect their materials and to assume determinate forms. Within the last few years, however, our ideas of vital processes have undergone profound modifications; and the interest, and even disquietude, which the change has excited are amply evidenced by the discussions and protests which are now common, regarding the phenomena of vitality. In tracing these phenomena through all their moidfications, the most advanced philosophers of the present day declare that they ultimately arrive at a single source of power, from which all vital energy is derived; and the disquieting circumstance is that this source is not the direct fiat of a supernatural agent, but a reservoir of what, if we do not accept the creed of Zoroaster, must be regarded as inorganic force. In short, it is considered as proved that all the energy which we derive from plants and animals is drawn from the sun. '
"A few years ago, when the sun was affirmed to be the source of life, nine out of ten of those who are alarmed by the form which this assertion has latterly assumed would have assented, in a general way, to its correctness. Their assent, however, was more poetic than scientific, and they were by no means prepared to see a rigid mechanical signification attached to their words. This, however, is the peculiarity of modern conclusions: that there is no creative energy whatever in the vegetable or animal organism, but that all the power which we obtain from the muscles of man and animals, as much as that which we develop by the combustion of wood or coal, has been produced at the sun's expense.
"To most minds, however, the energy of light and heat presents itself as a thing totally distinct from ordinary mechanical energy. Either of them can nevertheless be derived from the other. Wood can be raised by friction to the temperature of ignition; while by properly striking a piece of iron a skilful blacksmith can cause it to glow. Thus, by the rude agency of his hammer, he generates light and heat. This action, if carried far enough, would produce the light and heat of the sun. In fact, the sun's light and heat have actually been referred to the fall of meteoric matter upon his surface; and whether the sun is thus supported or not, it is perfectly certain that he might be thus supported. If, then, solar light and heat can be produced by the impact of dead matter, and if from the light and heat thus produced we can derive the energies which we have been accustomed to call vital, it indubitably follows that vital energy may have a proximately mechanical origin.
"In what sense, then, is the sun to be regarded as the origin of the energy derivable from plants and animals? Let us try and give an intelligible answer to this question. Water may be raised from the sea-level to a high elevation, and then permitted to descend. In descending it may be made to assume various forms--to fall in cascades, to spurt in fountains, to boil in eddies, or to flow tranquilly along a uniform bed. It may, moreover, be caused to set complex machinery in motion, to turn millstones, throw shuttles, work saws and hammers, and drive piles. But every form of power here indicated would be derived from the original power expended in raising the water to the height from which it fell. There is no energy generated by the machinery : the work performed by the water in descending is merely the parceling out and distribution of the work expended in raising it.
"In precisely this sense is all the energy of plants and animals the parceling out and distribution of a power originally exerted by the sun. In the case of the water, the source of the power consists in the forcible separation of a quantity of the liquid from a low level of the earth's surface, and its elevation to a higher position, the power thus expended being returned by the water in its descent. In the case of vital phenomena, the source of power consists in the forcible separation of the atoms of compound substances by the sun. We name the force which draws the water earthward 'gravity,' and that which draws atoms together 'chemical affinity' ; but these different names must not mislead us regarding the qualitative identity of the two forces. They are both attractions ; and, to the intellect, the falling of carbon atoms against oxygen atoms is not more difficult of conception than the falling of water to the earth.
"The building up of the vegetable, then, is effected by the sun, through the reduction of chemical compounds. The phenomena of animal life are more or less complicated reversals of these processes of reduction. We eat the vegetable, and we breathe the oxygen of the air; and in our bodies the oxygen, which had been lifted from the carbon and hydrogen by the action of the sun, again falls toward them, producing animal heat and developing animal forms. Through the most complicated phenomena of vitality this law runs : the vegetable is produced while a weight rises, the animal is produced while a weight falls.
"But the question is not exhausted here. The water employed in our first illustration generates all the motion displayed in its descent, but the form of the motion depends on the character of the machinery interposed in the path of the water. In a similar way, the primary action of the sun's rays is qualified by the atoms and molecules among which their energy is distributed. Molecular forces determine the form which the solar energy will assume. In the separation of the carbon and oxygen this energy may he so conditioned as to result in one case in the formation of a cabbage, and in another case in the formation of an oak. So also, as regards the reunion of the carbon and the oxygen, the molecular machinery through which the combining energy acts may, in one case, weave the texture of a frog, while in another it may weave the texture of a man.
"The matter of the animal body is that of inorganic nature. There is no substance in the animal tissues which is not primarily derived from the rocks, the water and the air. Are the forces of organic matter, then, different in kind from those of inorganic matter? The philosophy of the present day negatives the question. It is the compounding, in the organic world, of forces belonging equally to the inorganic, that constitutes the mystery and the miracle of vitality. Every portion of every animal body may be reduced to purely inorganic matter. A perfect reversal of this process of reduction would carry us from the inorganic to the organic; and such a reversal is at least conceivable. The tendency, indeed, of modern science is to break down the wall of partition between organic and inorganic, and to reduce both to the operation of forces which are the same in kind, but which are differently compounded.
"Consider the question of personal identity, in relation to that of molecular form. Thirty-four years ago, Mayer of Heilbronn, with that power of genius which breathes large meanings into scanty facts, pointed out that the blood was 'the oil of the lamp of life,' the combustion of which sustains muscular action. The muscles are the machinery by which the dynamic power of the blood is brought into play. Thus the blood is consumed. But the whole body, tho more slowly than the blood, wastes also, so that after a certain number of years it is entirely renewed. How is the sense of personal identity maintained across this flight of molecules? To man, as we know him, matter is necessary to consciousness ; but the matter of any period may be all changed, while consciousness exhibits no solution of continuity. Like changing sentinels, the oxygen, hydrogen and carbon that depart seem to whisper their secret to their comrades that arrive, and thus, while the Non-ego shifts, the Ego remains the same. Constancy of form in the grouping of the molecules, and not constancy of the molecules themselves, is the correlative of this constancy of perception. Life is a wave which in no two consecutive moments of its existence is composed of the same particles.
"Supposing, then, the molecules of the human body, instead of replacing others, and thus renewing a preexisting form, to be gathered first hand from nature and put together in the same relative positions as those which they occupy in the body. Supposing them to have the selfsame forces and distribution of forces, the selfsame motions and distribution of motions would this organized concourse of molecules stand before us as a sentient thinking being? There seems no valid reason to believe that it would not. Or, supposing a planet carved from the sun, set spinning round an axis, and revolving round the sun at a distance from him equal to that of our earth, would one of the consequences of its refrigeration be the development of organic forms? I lean to the affirmative. Structural forces are certainly in the mass, whether or not those forces reach to the extent of forming a plant or an animal. In an amorphous drop of water lie latent all the marvels of crystalline force ; and who will set limits to the possible play of molecules in a cooling planet? If these statements startle, it is because matter has been defined and maligned by philosophers and theologians, who were equally unaware that it is, at bottom, essentially mystical and transcendental."
Summarizing the foregoing discussion concerning the nature and general conditions of life and living matter, the fact stands out clearly and distinctly that life from its beginning has been dependent upon the external conditions of the earth's surface. In a mathematical sense, life is a function of the earth's development. Living sub-stance could not exist while the earth was a molten sphere without a solid, cool crust; it was obliged to appear with the same inevitable necessity as a chemical combination, when the necessary conditions were given, and it was obliged to change its form and its composition in the same measure as the external conditions of life changed in the course of the earth's development. It is only a portion of the earth's matter.
The combination of this matter into living substance was as much the necessary product of the earth's development as was the origin of water. It was an inevitable result of the progressive cooling of the masses that formed'' the earth's crust. Likewise, the chemical, physical and morphological characteristics of existing living substance are the necessary result of the influence of the external conditions of life upon the internal relations of past living substance. Internal and external vital conditions are in-separably correlated and the expression of this correlation is life.
The artificial production of life would thus seem a theoretical possibility. It has been several times suggested in the discussion of the chemical aspects of life that living matter may sooner or later be produced in the chemists' laboratories. However improbable this suggestion may seem, there are many facts which point to its possibility. Heraclitus compared life with fire. Such a comparison is a pertinent one. Consideration of vital conditions makes this more evident. "It has been shown that life," to quote Verworn, "like fire, is a phenomenon of nature which appears as soon as the complex of its conditions is fulfilled.
"If these conditions are all realized, life must appear with the same necessity as fire appears when its conditions are realized; likewise life must cease as soon as the complex of its conditions has undergone disturbance and with the same necessity with which fire is extinguished when the conditions for its maintenance cease. If, therefore, all vital conditions had been investigated in their minutest details, and it were possible artificially to establish them exactly, life would be produced synthetically, just as fire is produced, and the ideal that existed in the imagination of the medieval alchemists in their attempted production of the homunculus would be achieved."
But, notwithstanding the fact that this theoretical possibility cannot be denied, every attempt at the present time to produce life artificially and to imitate in the laboratory the obscure act of spontaneous generation must appear preposterous. So long as knowledge of the composition of living substance is so imperfect as it is now, the attempt artificially to compound living substance will be like the undertaking of an engineer to put together a machine, the most important parts of which are wanting. For the present the task of physiology can consist only in the investigation of life. When physiology shall actually have accomplished this, it may think of testing the completeness and correctness of its achievement by the artificial creation of life.
The nature of life has become better understood by the study of death, which to the biologist is simply the cessation of the activities of life. In the first place it is some-times extremely difficult to distinguish between life and apparent death. Several illustrations will make this clear. In India, where mystery and magic have always prevailed, the belief seems to have existed for a long time that many men, especially the so-called fakirs whose existences are full of privation and self-inflicted torture and who are supposed to possess special holiness, have the remarkable power of voluntarily putting a complete stop to their lives for a time and later resuming them undisturbed and unchanged. A great number of such cases, in which the fakirs have been buried in this condition of suspended animation and after some time have been taken from their graves, have been reported by travelers from India.
It is not to be denied that these tales, especially those of the Indian fakirs, are calculated to awaken distrust, and a sound skepticism is the basis of all good criticism. If, however, from all the known stories their more or less sensational accompaniments be removed, the simple statement remains that certain men can voluntarily put themselves into a state in which no vital phenomena are demonstrable by a more or less superficial examination and can awaken later to normal life. Now sufficient cases are known where physicians by the usual methods of their practice are able to discover absolutely no traces of vital phenomena, where pulse, respiration, movement and irritability are not to be observed; and yet where the person, supposedly dead, has after a time returned to life.
These phenomena are usually termed 'apparent death' and are connected with those of normal sleep by a series of transition phenomena. Such transition phenomena are the continual sleep in which persons, such as the 'sleeping soldier' and the 'sleeping miner' (authenticated medical cases), continue in a state of depressed vital activity and are absolutely incapable of being awakened, and especially the phenomena of the winter sleep of warm-blooded animals.
However doubtful may be the reported powers of representatives of the vertebrate (or backboned) animals to suspend for a time all vital phenomena, there is no longer any question that many of the lower animals have this power highly developed. As long ago as 1719 Leeuwenhock, the famous improver of the microscope, discovered that small animals, now known as rotifers, may be dried completely to dust and again restored to active life by being placed in water. One of the most remarkable cases of this kind described by Verworn is that of the tardigrade, or bear animalcule, which, so long as it is in water, performs all its vital phenomena like other animal;. "But if it be isolated and allowed to dry slowly upon a slide, it is seen that the more the water evaporates the slower become its movements, until finally they cease entirely when the drop is dried up. Then the body gradually shrinks, the skin become wrinkled and folded, the form becomes gradually indistinguishable, and some time after the animal has become dried it can scarcely be distinguished from a grain of sand. In this dried condition it can remain for many years without undergoing the slightest change. If it be moistened again with water, the return of life to the desiccated body after its sleep can be followed with the microscope. The awakening of the tardigrade or the anabiosis, as Preyer has termed the process, takes place somewhat as follows : The body swells up and be-comes extended, the folds and wrinkles slowly disappear, the extremities project and the animal soon assumes its normal shape." At first it remains quiet; then, after a time, varying, according to the duration of the drying, from a quarter of an hour to several hours, movements. at first slow and feeble, begin and gradually become stronger and more frequent until after some time the animal, unaided, creeps away to resume life at the point where it was interrupted.
Likewise the seeds of many plants retain their power of germination for long periods of time. Here it might be well to add that the well known story that wheat seeds taken from the graves of Egyptian mummies will germinate, tho thousands of years old, has been disproved by Mariette, the famous Egyptologist. However, from many observations it seems certain that many plant seeds, when completely dried, can retain their power to germinate for more than a hundred or perhaps two hundred years. These rare facts are of great importance in forming a conception of life and demand exhaustive investigation. The question to be considered is whether it is allowable to regard organisms in this peculiar condition as really lifeless.
It has been pointed out in the earlier part of this chapter that it is metabolism in which the living organism differs from lifeless matter. But this is difficult to settle in some of the concrete cases mentioned above. Do dust dry animals and seeds possess no metabolism or is this metabolism so depressed or so slight that investigation cannot determine whether the life process is at a standstill or whether a 'vita minima' exists? Delicate experiments within the last twenty years show no evidence of the use of oxygen or the production of carbonic acid or other products of metabolism in dried organisms sealed for months in air-tight tubes.
From the results of these experiments it can no longer be doubted that in desiccated organisms there is a complete standstill of life. Can organisms in this peculiar condition be termed dead? In reality they are lifeless but not dead, for anabiosis is possible after the application of water, while nothing can Bring dead organisms back to life. The distinction between the dried and the dead organism lies in the fact that in the former all the internal vital conditions are still fulfilled and only the external conditions in part have appeared, while in the latter the internal vital conditions have experienced irreparable disturbances, altho the external conditions can still be fulfilled.
Preyer. illustrates this distinction very happily. He compares the dried organism to a clock that has been wound but has stopped, so that it needs only a push to set it going, and the dead organism to a clock that is broken and cannot be made to go by a push. Hence a sharp distinction must be made between dried and dead organisms. But dried organisms cannot be called living, for they exhibit no vital phenomena, and, as has been seen, vital phenomena are the criterion of life. It is best, therefore, to apply to them the expression 'apparently dead.'
Still more difficult than cases of apparent death is the determination of an exact limit between life and active death. In daily life it is easy to distinguish the dead organism from the living, for from the human body and from the higher animals a general conception of death has been formed and it is usual to consider it as occurring at the moment when the heart, hitherto never quiet, stands still and the individual ceases to breathe. But this is merely following the superficial habits of daily life and taking into consideration only the gross differences that make their appearance at that time, without noticing the continuance of certain phenomena after this all-important moment.
The criterion of life is formed only by the vital phenomena i.e., by the various phases in which the vital process, or the metabolism, becomes evident to the senses. But if this criterion be applied to he human being at the moment usually termed the moment of death, it is found that in reality be is not dead.
It is true that the spontaneous gross muscular movements cease, the man becomes relaxed and quiet. But the muscles frequently remain for several hours sensitive to external influences, responding to the latter with twitchings and movements of the limbs, in other words, showing vital phenomena. A moment even comes when the muscles gradually contract once more spontaneously, this is the death-stiffening (rigor mortis). Not until this has passed is the life of the muscles extinguished. Nevertheless, even then the body is not entirely dead. Certain parts only, certain organs or cell-complexes, such as the cells of the nervous system and of the muscles, no longer show vital phenomena ; but other cells and cell-complexes continue to live unchanged long after rigor mortis has passed.
What moment then shall be designated as the moment of death? If the existence of vital phenomena be employed as the criterion, then the moment when spontaneous muscular movement, especially the activity of the heart, ceases, cannot consistently be regarded as the moment of death, for other cell-complexes continue to live for a long time thereafter. It is evident, therefore, that there is no definite point of time at which life ceases and death begins; but there is a gradual passage from normal life to complete death which frequently begins to be noticeable during the course of a disease. Death is developed out of life,
It is true that the above example is that of a highly complicated organism. But even in the lowest and simplest microscopic organisms death comes on gradually, and, as in the higher animals, is the end-result of a long series of processes which begin with an irreparable injury to the normal body and lead, step by step, to complete cessation of life activities. To this series of stages in the development of death Schultze and Virchow (1870), famous in pathology, have given the term 'necrobiosis,' the gradual transition between life and death.
It is seen, therefore, that it is impossible to draw a sharp line between life and death, that life and death are only the two end results of a long series of changes which run their course successively in the organism. "But if, after having established this fact," says Verworn, "the transition stages be left out of consideration for the moment and only the two end-results be considered, on the one side, the uninjured living organism and, on the other, the same organism killed and preserved in alcohol by the modern technical methods, a sharp distinction between these two can be recognised in the fact that in the former the life-process goes on undisturbed, as is evident from the appearance of all vital phenomena, while in the latter it is forever at a complete standstill, as is shown by the absence of even the slightest phenomena of life."