CHAPTER VI.NUTRITION.
FUNCTIONAL ASSIMILATION. FUNCTIONAL DESTRUCTION. ORGANIC DESTRUCTION. ASSIMILATING SYNTHESIS.
The extreme importance of nutrition—§ 1. Effect of vital activity—Destruction or growth—Distinction between the living substance and the reserve-stuff mingled with it—Organic destruction—Destruction of reserve-stuff—Destruction of living matter—Growth of living matter—§ 2. The two categories of vital phenomena—Foundations of the idea of functional destruction—The two kinds of phenomena of vitality—Criticism of Claude Bernard—Current views—Criticism of Le Dantec’s new theory of life.—§ 3. Correlation of the two kinds of vital facts—Law of connection—Contradictions in the new theory.—§ 4. The characteristics of nutrition—Its definition—Its permanence—Erroneous idea of the vital vortex—Formative assimilation of reserve-stuff—Formative assimilation of protoplasm—Death, real and apparent.
The Immense Importance of Nutrition.—We now come to the important feature of vitality. All other characteristics of living matter, its unstable equilibrium, its chemical and anatomical organization, the acquisition and the maintenance of a typical form, are only secondary properties, so to speak, subordinate with reference tonutrition. Generation itself is only a mode.Nutritionis the essential attribute of life. It is life itself.
Before we define it a few preliminary explanations are necessary.
The most striking thing in living matter is itsgrowth. An animal, a vegetable, is something which is first more or less minute, and which grows. Its characteristic is to expand—from the spore, the seed, the slip, the egg—it grows.
Whether we are dealing with a cellular element, a plastid, or a complex being, their condition is the same in this respect. No doubt when the animal or plant has reached a certain stage of development its growth is stopped, and for a more or less lengthy period it remains in the adult stage, in what seems to be equilibrium. But even then there is no check in the manufacture of living matter; there is only a compensation between its production and its destruction.
It is important to reduce to order the ideas on this important subject, which at present are confused, inconsistent, and contradictory. In biology grievous confusion reigns.
Distinction between the Living Substance and the Reserve-stuff mingled with it.—The physiology of nutrition has given rise to a vast body of research during the last half-century. Physiological schools, masters and pupils, such as the school at Munich under Voit and Pettenkofer, Pflüger’s at Bonn, Rubner’s, and those of Zuntz and von Noorden at Berlin, and a large number of zootechnical and agricultural laboratories through the whole world have foryears past been engaged in analyzing ingesta and egesta, in drawing up schedules of nutrition, in order to determine the course of decomposition and reconstitution of the living material.
If I were asked what, in my opinion, is the most general result of all this labour, I would reply that it has affirmed and corroborated the important distinction which must be drawn betweenliving substance, properly so called, andreserve-stuff. The latter, thereserve-stuffof albuminoids, carbohydrates, and fats, are so intimately intermingled with the living substance that they are in most cases very difficult to distinguish from it.
Organic Destruction.—A second point, which is placed equally beyond doubt, is that the vital functional activity is accompanied by a destruction of the immediate principles of the organism, in the direction of their simplification. This functional destruction cannot be doubted in the case of differentiated organs in which the functional activity is evident, intermittent, and in some measure distinct from the other vital phenomena which take place in them. For example, in the case of contracting muscles the respiratory carbonic acid and urinary carbon are the irrefutable proofs of this destruction: weak in repose, abundant during activity, and in proportion to it. There can be no doubt on this point. The truth laid down by Claude Bernard under the name of thelaw of functional destructionhas been doubly consecrated by experiment and theory. According to the energetic theory, in fact, mechanical and thermal energies manifested in the vital functional activity can only have their source in the chemical energy set free by the destruction of the immediateprinciples of the organism, reduced to a lower degree of complexity.
Destruction of Reserve-stuff.—But now the disagreement begins. What are these decomposed, destroyed principles? Do they belong to the cellular reserve-stuff or to the living matter properly so called? There is no doubt that most of them belong to the reserve-stuff. For example, this is especially true of glycogen, which is consumed in muscular contraction just as coal is consumed in the furnace of the locomotive; and glycogen is a reserve-stuff of muscle. These reserve-stuffs destroyed in the functional activity can be built up again only during repose.
But it is not yet certain whether the living matter itself, the active protoplasm, the muscular protoplasm, takes part in this destruction, whether it provides it with elements. Experiments have proved contradictory. Experimenters have isolated the nitrogenous wastes (urea) after muscular labour, and they have compared them with the wastes of the period of repose. These nitrogenous wastes bear witness to the destruction of albuminoid substances, and the latter are the constituent principles of living matter. If—under conditions of sufficient alimentation—the muscular functional activity involves more nitrogenous waste,i.e., a greater destruction of albuminoids, it might be supposed that the living material properly so called has been used up and destroyed for its own purposes. (And here again there might be a reserve-stuff of albuminoids, distinct from the living protoplasm itself, and more or less incorporated with it.)
But experiment so far has not given decisive results. The latest experimental researches, such as those ofIgo Kaup, of Vienna, which date from 1902, tell us as uncertain a tale as their predecessors. The increase in the destruction of albumen has not been constant; the conditions of the observations do not justify our making an assertion eitherproorcon.
Destruction of Living Matter.—As no certain answer is supplied by experiment, theory intervenes and gives two conflicting answers. The majority of physiologists are inclined to believe inthe destruction of the living substance as the result of its own functional activity. The functional activity would therefore destroy not only the reserve-stuff, but also the protoplasmic material. This is the current view. Only this opinion is strongly challenged by the positive teaching of science. It is certain that this material, in the muscle, is but little attacked, if it is attacked at all. We have seen above that the physiologists, with Pflüger and Chauveau, are agreed on this point. The vital functional activity in particular is destructive to the reserve-stuffs. It does not destroy them much; it destroys the organic material still less. Both would be repaired in functional repose.
Growth of Living Matter.—The second assertion is diametrically opposed to this. Not only, says Le Dantec, is the muscle not destroyed in the functional activity, but it grows. Contrary to universal opinion, the protoplasmic material increases by activity, and it is destroyed in repose. There would thus be a general law—the law of functional assimilation. “A cell of brewers’ yeast when introduced into a sugared must makes this must ferment, and at the same time, so far from destroying it, it increases it. Now, the fermentation of the must is exactly the same as thefunctional activity of the yeast.” It is, says the same author, a mistake to believe that the phenomena of functional activity, ofvital activity, only takes place at the price of organic destruction. Here, then, are these two competing views. They are not so very far apart as a matter of fact, since the question at issue is one of deciding between a slight destruction and a slight growth, but theoretically they are strongly opposed. Moreover, they are arbitrary, andexperimenthas not decided between them.
Foundation of the Idea of Functional Destruction. Claude Bernard.—The doctrine of functional destruction has been laid down with remarkable power by Claude Bernard. But the terms in which he has expressed it in a measure betray the thoughts of the great physiologist, or, at any rate, overstep the immediate fact he had in view. “The phenomena of destruction are very obvious. When movement is produced, when the muscle contracts, when volition and sensibility are manifested, when thought is exercised, when the gland secretes, then the substance of the muscles, of the nerves, of the brain, of the glandular tissue, becomes disorganized, destroyed, and consumed. So that every manifestation of a phenomenon in the living being is necessarily connected with an organic destruction.” To Claude Bernard organic destruction is a truth. To Le Dantec it is an error. Which is right? Clearly Claude Bernard. He bases his conviction on the analyses of the materials excreted in the process of physiological work. The excreta bear witness to a certain organic demolition. Generalizing this teaching of experiment the illustrious biologist divined the fundamental law of energetics before the idea of energetics had made much way in France. Every act which expends energy, which produces heat or motion, any manifestation whatever that may be looked upon as an energetic transformation, necessarily expends energy, and that energy is borrowed from the substance of the organism. These substances are simplified, broken up, and destroyed. Now the functional activity of the muscle produces heat and movement in warm-blooded as well as in cold-blooded animals. The functional activity of the glands produces heat, as has been shown by the celebrated experiments of C. Ludwig on the salivary secretion, and as is also shown by the study of thermal topography in the vertebrates. The functional activity of the nerves and the brain produces a slight quantity of electricity and heat, as most observers have agreed. The functional activity of the electrical and of the photic apparatus also expends energy. Finally, the eye which receives the photic impression destroys the purple matter of the retina, and that purple matter, as we well know, is recuperated in the dark during the repose of the organ. Everything that is expressed objectively, everything that is a phenomenon in the living being—with the exception of growth and formation, which are generally slow phenomena, and of which we can only get an idea by the comparison of successive states—all these energetic manifestations suppose a destruction of organic matter, a chemical simplification, the source of the energy manifested. And that is why material destruction does not merelycoincide with functional activity, but is its measure and expression.
The Two Kinds of Phenomena of Vitality.—Another point on which Claude Bernard is right and his opponent is wrong is not less fundamental. What are we to understand by functional phenomena? This is the very point at issue. Now, in the mind of physiologists, this expression has a perfectly definite meaning. It is not so with Le Dantec. Physiologists who have studied animals rather high in organization—in which the differentiation of phenomena enables us to grasp the fundamental distinction—have readily recognized that the phenomena of living beings are divided into two categories. There are some which are intermittent, alternative, which take place, or grow stronger at certain moments, but which cannot be continuous—they are thefunctional acts; there are others in which this characteristic of explosives, energetic expenditure and intermittence, do not appear—they are, in general, thenutritive acts. The muscle which contracts shows functional activity. It has an activity and a repose. During this apparent repose we must not say that it is dead; it has a life, but that life is obscure as far as the salient fact of functional movement is concerned. The salivary gland which throws up waves of saliva when the food is introduced and masticated in the mouth, or when the chord of the tympanum is at work, is in a state of functional activity; this is the salient phenomenon. But before, though nothing, absolutely nothing, was flowing through the glandular canal, yet the gland was not reduced to the condition of a dead organ: it was living a more obscure, a less evident life. The microscopical researches of Kühne, Lea, and Langley,now universally verified, show us that during this time of apparent repose the cells were loading up their granulations and getting ready the materials of secretion, as just now the muscle at rest was accumulating glycogen and the reserve-stuff which are to be expended and destroyed in contraction. Similarly, with regard to the functional activity of the other glands, of the brain, etc. Claude Bernard was, therefore, perfectly right, when he took as his model the chemists who distinguished between exothermic and endothermic reactions, and who classed the phenomena of life into two great divisions: those of functional activity, and those of functional repose.
1st.The phenomena of functional activity“are those which ‘leap to the eyes,’ and by which we are inclined to characterize life. They are conditioned by the effects of wear and tear, of chemical simplication, and of the organic destruction which liberates energy.” And it must be so, because these functional manifestations expend energy. These phenomena, which are the most obvious, are also the least specific phenomena of vitality. They form part of the general phenomenality.
2nd. Thephenomenawhich accompanyfunctional reposecorrespond to the building up of the reserve-stuff destroyed in the preceding period, to the organizing synthesis. The latter remains “internal, silent, concealed in its phenomenal expression, noiselessly gathering together the materials which will be expended. We do not see these phenomena of organization directly. The histologist and the embryogenist alone, following the development of the element or of the living being, sees the changes and the phases which reveal this silent effort. Hereis a store of substance; there, the formation of an envelope or a nucleus; there, a division or multiplication, a renewal.” This type of phenomena is the only type which has no direct analogues: it is peculiar, special to the living being: what is really vital is this evolutive synthesis. Life is creation.
Criticism of Claude Bernard.—All this is perfectly true. Thirty years of the most intensive scientific development have run by since these lines were written, and have not essentially changed the ideas therein expressed. His work in its broad lines remains intact. Does that imply, however, that everything is perfect in detail and expression, and that there is no reason for making it more precise or for giving it fresh form? No doubt this is not so. Although Claude Bernard contributed to establish the essential distinction between the real living protoplasm and the materials of reserve-stuff which it contains, he has not drawn a sufficiently clear distinction between what belongs to each of the categories. He has not specified, in relation to organic destruction, what bearing it has on the organic materials of reserve-stuff. Sometimes he uses the term “organic destruction,” which is correct, and sometimes “vital destruction,” which is of doubtful import. Further, he employs an obscure and paradoxical formula to characterize the obvious but nevertheless not specific phenomena of organic destruction, and he says: “life is death.”
Current Views.—Nowadays, if I may express a personal opinion on this important distinction between functional activity and functional repose, I should say that after having distinguished betweenthe two categories of phenomena we must try to correlate them. We must try to discover, for instance, what there is in common between the muscle in repose and the muscle in contraction, and to perceive in themuscular tonusa kind of bridge thrown between these two conditions. The functional activity would be uninterrupted, but it would have its degrees of activity. The muscular tonus would be the permanent condition of an activity which is capable only of being considerably raised or lowered. Similarly for the glandular functional activity; the periods of charge must be connected with the periods of discharge. In a word, following the constant path of the human mind in scientific knowledge, after having drawn the distinctions that are necessary to our understanding of things, we must obliterate them. After having dug our ditches we must fill them up again. After having analyzed we must synthesize. The distinction between the phenomena offunctional activityand the phenomena offunctional reposeorpurely vegetativeand nutritiveactivity, though only valid in the case of a provisional and approximate truth, none the less throws light on the obscure regions of biology.
The succession of energy and repose, of sleep and awakening, is a universal law, or at least a very general law, connected with the laws of energetics. The heart, the lungs, the muscles, the glands, the brain obey in the most obvious manner this obligation of rhythmical activity. The reason is clear. It is because the functional activity involves what is generally a sudden expenditure of energy, and this has to be replaced by what is generally a slow process of reparation. Functional activity is anexplosive destruction of a chemical reserve which is built up again more or less slowly.
Criticism of Le Dantec’s “New Theory of Life.”—Let us now examine the antithesis of Claude Bernard’s views. There are evidently rudimentary organisms in which the differentiation of the two categories of phenomena is but little marked; in which, apart from the movement, it is impossible to recognize intermittent, functional activities clearly distinct from morphogenic activity. It is not in this domain of the indistinct that we must seek the touchstone of physiological distinctions. Clearly, we must not choose these elementary plastids to test the doctrine of functional assimilation and functional destruction. But is not this exactly what Le Dantec did when he began his researches on brewers’ yeast? When we try to examine things, we must choose the conditions under which they are differentiated, and not those in which they are confused. And this is why, in the significant words of Auguste Comte, “the more complex living beings are, the better known they are to us.” The philosopher goes still farther in this direction, and adds “directly it is a question of the characteristics of animality we must start from the man, and see how those characteristics are little by little degraded, rather than start from the sponge and endeavour to discover how these characteristics are developed. The animal life of the man assists us to understand the life of the sponge, but the converse is not true.”
When, moreover, we consider a vegetable organism such as yeast, which derives its energy, not from itself, not from the potential chemical energy of its reserve-stuff, but directly from the medium—that isto say, from the potential chemical energy of the compounds which form its medium of culture,—we then find ourselves in the worst possible situation for the recognition of organic destruction. Further, it is doubly wrong to assert that in so ill-chosen a type the functional phenomena do not result from an organic destruction—for at first there are no very distinct functional phenomena here—and, in the second place, there certainly is organic destruction. The phenomena of the morphogenic vitality detected in the yeast are the exact concomitants, or the results, of the destruction of an organic compound, which in this case is sugar. The yeast destroys an immediate principle, and this is the point of departure of its vital manifestations; only, it has not, as a preliminary, clearly incorporated and assimilated this principle. When, therefore, the functional phenomena are effaced and disappear, we none the less find phenomena of destruction of organic compounds which are in a measure, a preface to the phenomena of growth. This is what happens in the case of brewers’ yeast: and here, again, the two categories of facts exist. Once more, we find, in the first place, the phenomena of destruction (destruction of sugar, reduced by simplification to alcohol and carbonic acid)—phenomena which this time no longer respond to obvious functional manifestations; and, in the second place, the phenomena of chemical and organogenic synthesis, corresponding to the growth of the yeast and the multiplication of its protoplasm. The former are no longer detected, as we have just said, by striking manifestations. However, it is not true that everything which is visible and which may be isolated outside the activity of the yeast is part of thosephenomena. The boiling of the juice or the mash, the heat given off by the copper, all this phenomenal apparatus is but the consequence of the production of the carbonic acid and of its liberations—i.e., the consequence of the act of destruction of the sugar. Here is organic destruction with its energetic manifestations!
This example of the life of brewers’ yeast, of the saccharomyces, specially chosen by Le Dantec as being absolutely clear and giving the best illustration of his argument, contradicts him at every point. The general thesis of this vigorous thinker is that we cannot distinguish between the two parts of the vital act, organic destruction, and assimilating synthesis; that these two acts are not successive; that they give rise to phenomenal manifestations equally evident, apparent, or striking. Now, in the case of yeast, the phenomenon of destruction is clearly distinct from that of the assimilating synthesis which multiplies the substance of the saccharomyces. In fact, the action is realized by means of an alcoholic diastase manufactured by the cell; and Büchner succeeded in isolating this alcoholic ferment which splits up the sugar into alcohol and carbonic acid, and alsoin vitroandin vivo, makes the vat boil and heats the liquid. All the yeast is at work at once, says M. Dantec. No, and this is the proof.
And, further, Pasteur himself, who had shown the relation of the decomposition of the sugar to the fact of the growth of the yeast and of the production of accessory substances such as succinic acid and glycerine, always referred tocorrelationbetween these phenomena. The destruction of the sugar is thecorrelativeof the life of the yeast. This was hisfavourite formula. It never entered his head that there could be a confusion instead of a correlation, and that there might be only one and the same act, the phases of which would be indistinguishable. This unfortunate idea, which was fated to be so rapidly contradicted, is due to Le Dantec. Far from it being the case, Pasteur had distinguished theferment functionfrom the life of the yeast. According to him, the yeast may exist sometimes as a ferment and sometimes otherwise.
It is this correlation between actsdistinct in themselvesbutusually connectedthat was announced by Claude Bernard. And,mirabile dictu—and this is the natural outcome of the perfect sanity of mind of this great physiologist—it happens that not only Pasteur’s researches, but the development of a new science, Energetics, and Büchner’s discovery lend support to his views, and that, too, in a field where one would have thought they had no application. Le Dantec is wrong when he declares that these ideas only apply to vertebrates. “It is clear,” he says on several occasions, “that the author has in view the metazoa and even the vertebrates.” Well! no. All that is general, universally applicable, and universally true. So that there are two orders of distinct phenomena energetically opposed and certainly connected. We need only repeat Claude Bernard’s own words quoted by Le Dantec in order to confute them.
Law of Connection of Two Orders of Vital Facts.—“These phenomena [of organic destruction and ofassimilating synthesis] are simultaneously produced in every living being, in a connection which cannot be broken. The disorganization or dissimilation uses up living matter [by this we must understand the reserve-stuff, as will be seen later on in the quotation] in the organsin function: the assimilating synthesis regenerates the tissues; it gathers together the reserve-stuff which the vital activity must expend. These two operations of destruction and renovation, inverse the one to the other, are absolutely connected and inseparable, in this sense at any rate, that destruction is the necessary condition of renovation. The phenomena of functional destruction are themselves the precursors and the instigators of material regeneration, of the formative process which is silently going on in the intimacy of the tissues. The losses are repaired as they take place; and equilibrium being re-established as soon as it tends to be broken, the body is maintained in its composition.”
It is perfectly right and wise to say with Claude Bernard that the two orders of facts are successive, and that one is normally the inciting condition of the other. The possibility of the development of the yeast when fermentation fails, and the weakness of this development on the other hand under these conditions, are an excellent proof of this. The one proves the essential independence of the two orders of facts, the other the inciting and provoking virtue of the first relatively to the second. The experimental truth is thus expressed with a minimum of uncertainty. We know the facts which led Le Dantec to formulate his law of functional assimilation—namely, that the functional activity is useful or indispensable to the growth of the organ; that the organs which arefunctionally active grow, and those which do not act become atrophied. We are only expressing the facts when we say that the organic destructions that go on in the living being (whether at the expense of its reserve-stuff or at the expense of its medium, or whether it be even slightly at the expense of the plastic substance itself) are the antecedent, the inciting agent or the normal condition of the chemical and organogenic syntheses which create the new protoplasm.
On the other hand, we are wrong if we hold with Le Dantec that instead of two chemical operations there is only one, that which creates the new protoplasm. The obvious destruction is neglected; it is deliberately passed over. He does not see that it is necessary to liberate the energy employed in the construction, by complication, of this highly complex substance which is the new protoplasm. He really seems to have made up his mind not to analyze the phenomenon. If we decline to admit that to the first act of functional destruction succeeds a second, assimilation or organogenic synthesis, we are looking at elementary beings, in which the succession cannot be grasped, as we look on brewers’ yeast. We not only mean that the morphogenic assimilation results from the functional activity; we mean that it results from it directly, immediately, that it is the functional activity itself. Experiment tells us nothing of all this. It shows us the real facts, the facts of the destruction of an organic immediate principle, the sugar, and the fact that an assimilating synthesis is the correlative of this destruction. Besides, if it is impossible in examples of this kind to exhibit the succession, it is perfectly easy in beings of a higher order. It is, then, clearly seen that the preliminarydestruction of a reserve-stuff (and perhaps of a small quantity of the living substance) precedes and conditions the formation of a greater quantity of this living matter—in other words, the growth of the protoplasm of the organ.
Contradictions in the New Theory.—Moreover, these mistakes involve those who make them in a series of inextricable contradictions. Here, for example, is life; it is found, they say, in three forms:—Life manifested, or condition 1º; latent life, or condition 3º. So far this is the classical theory; but they add a condition 2º, which is what might be calledpathological or incomplete life. This is defined by the following characteristic:—That its functional phenomena are identical with those in the first form, but that they are not accompanied by assimilation and by protoplasmic growth, But since, they say, growth is the chemical consequence of the functional activity, since it is so to speak its metabolic aspect, since it is confused with it, and inseparable from it, by the argument—then it is contradictory and logically absurd to speak of condition 2º. It would be acknowledging in the case of the anucleated merozoite, for example, a functional activity unaccompanied by assimilation, yet identical with the functional activity which is accompanied by assimilation in the nucleated merozoite. The general movement, that of the cilia, the taking of food, the evacuation of the fæces, the contraction of the pulsatile vacuoles, are the same. And this fact is the best proof that this vital functional activity (with the organic destruction which is its energetic source) must be distinguished from the assimilation which usually follows it, and which in exceptional cases may not follow it.
We shall carry this discussion no farther. We have examined at some length Le Dantec’s views, and we have contrasted them with the doctrine which has been current in general physiology since the time of Claude Bernard, and this comparison does not turn out quite to their advantage. It was inevitable that the experimental and realistic spirit which inspired the doctrine of the celebrated physiologist made his work really too systematic. His formula, “life is death,” and the form he gave his ideas, are not always irreproachably correct. They lend themselves at times to criticism. Sometimes they require commentary. These are errors of detail which Le Dantec has summarized somewhat roughly. There is no necessity to do this in his own case. We pay our tribute to the clearness of his language, although we believe the foundations of his system are false and ill-founded. Their rigour is purely verbal. Their external qualities, their careful arrangement are well adapted to the seduction of the systematic mind prepared by mathematical teaching. This new theory of life is presented with pedagogic talent of the highest order. We think we have shown that the foundations are entirely fallacious, in particular the following:—Vital condition No. 2º; the confusion between functional activity and assimilating synthesis; the so-called absolute connection between morphogeny and chemical composition; the fundamental distinction between elementary life and individual life.
Definition of Nutrition.—As we have just seen, the organism is the scene of chemical reactions of twokinds, the one destructive and simplifying, the other synthetic, constructive, or assimilating. This totality of reactions constitutes nutrition. Hence the two phases that it is convenient to consider in this function—assimilationanddisassimilation. This twofold chemical movement ormetabolismcorresponding to the two categories of vital phenomena, of destruction (catabolism) and of synthesis (anabolism) is therefore the chemical sign of vitality in all its forms. But it is clear that disassimilation or organic destruction, which is destined to furnish energy to the organism for its different operations, reappears in the plan of the general phenomena of nature. It is not specifically vital in its principle. Assimilation, on the other hand, is in this respect much more characteristic.
To some physiologists nutrition is only assimilation. Of the two aspects of metabolism they consider only one, the most typical,Ad-similare, to assimilate, to restore the substance borrowed from the ambient medium, the alimentary substances,similarto living matter, to make living matter of them, to increase active protoplasm—this is indeed the most striking phenomenon of vitality. To grow, to increase, to expand, to invade, is the law of living matter. Assimilation, nutrition in its essentials, is, according to the definition of Ch. Robin, “the production by the living being of a substance identical with its own.” It is the act by which the living matter, the protoplasm of a given being, is created.
Permanence in Nutrition.—Nutrition presents one quite remarkable character—permanence. It is a vital manifestation, a property if we look at it in the cell, in the living substance, a function if we consider it in the animal or in the plant as a whole, which is neverarrested. Its suspension involvesipso factothe suspension of life itself. It is, in the words of Claude Bernard, that property of nutrition “which, as long as it exists in an element, compels us to believe that this element is alive, and which, when it is absent, compels us to believe that it is dead. It dominates all others by its generality and its importance. In a word, it is the absolute test of vitality.”
Biological Energetics shows the Importance of Nutrition.—We have indicated in advance the reason of its importance, showing that its two phases, disassimilation and assimilation, are the energetic condition of the two kinds of vital phenomena which we can distinguish.
Nutrition is a manufacture of protoplasm at the expense of the materials of the cellular ambient medium, which are assimilated—i.e., made chemically and physically similar to living matter and to the reserves it stores up. This operation, which is peculiarly chemical, is therefore indicated by the borrowing of materials from the external world, a borrowing which is always going on, because the operation is permanent, and, let me add, because of the continual rejection of the waste products of this manufacture. Our formula is:—Nutrition is a chemistry which persists.
The Idea of the Vital Vortex is Erroneous.—Here the effect has hidden the cause from the eyes of the biologists. They have been struck by the incessant entry and exit, by the never-ceasing passage, by thecycleof matter through the living being without guessing its why and wherefore; and they have taken as a picture of the living being a vortex in which the essential form is maintained while thematter, which is accessory, flows on without a check. This is Cuvier’svital vortex. But for what purpose is this circulating matter used? They thought that it was employed entirely for the reconstitution of the living substance, continually and inevitably destroyed by the vital Minotaur.
Destruction of Reserve-stuff.—Here again there is a mistake. Really living substance is but little destroyed, and consequently requires very little renewal by the functional activity of the animal machine. Its metabolism—destruction and renewal—is in every case infinitely less than is supposed in the classical image of the vital vortex. It is the merit of physiologists, and particularly of Pflüger and Chauveau, to have worked for nearly forty years to establish this truth. They have proved it, at least as far as the muscular tissue is concerned. Protoplasm, properly so-called, is only destroyed as the organs of a steam engine are destroyed—its tubes, its boiler, its furnace. And it matters little. We know that such an engine uses much coal, and we know very little of its machinery and its metallic frame. And so it is with the cell, the living machine. A very small portion of the food introduced will be assimilated in the living substance. By far the greater part of it is destined to be worked up by the protoplasm and placed in reserve under the form of glycogen, albumen, and fat, etc.—i.e., compounds which are not the really living substance, the hereditary protoplasm, but the products of its industry, just as they are or may be the products of the industry of the chemist working in his laboratory. They will be expended for the purpose of furnishing the necessary energy to the vital functional activity, muscularcontraction, secretion, heat, etc., just as coal is expended to set the steam engine going. The proof as far as the muscle is concerned does not stand alone. There are other examples. In particular, micrographic physiologists who have studied nervous phenomena say that the anatomical elements of the brain last indefinitely, and that they continue as they are, without renewal from birth to death. The permanence of the consciousness, be it said in passing, is connected by them with the permanence of the cerebral element (Marinesco).
Thus destruction is very restricted. There is only a very slight disassimilation of the living matter, properly so-called, in the course of the vital functional activity. We may even go farther than this experimental fact. This is what Le Dantec has done when he claims that there is even an assimilation, an increase of the protoplasm. Strictly speaking, this is possible, but there is no certain proof of it; and in any case we cannot agree with him when he affirms that the increase is thedirect resultof the functional activity and blends with it in one single, unique operation. We must, on the contrary, agree with Claude Bernard that it is only aconsequenceof it, that it is produced in consequence of the existence of a bond of correlation between organic destruction and assimilating synthesis.
Why is there this bond? That is easily understood if we reflect that the assimilating synthesis, an operation of endothermic, chemical complexity, naturally requires an exothermic counterpart, the organic destruction which will set free this necessary energy.
Formative Assimilation of Reserve-stuff. Formative Assimilation of Protoplasm.—It follows thatthere are in nutritive assimilation itself two distinct acts. The one consisting of the manufacture of reserve-stuff is the more obvious but the less specific; the other, really essential, is assimilation properly so-called, the reconstitution of the protoplasm. The former is indispensable to the production of the most prominent acts of vitality—movement, secretion, production of heat. If it is suspended, functional activity is arrested. We getapparent death, orlatent life. But if the real assimilation is arrested, we havereal death.
According to this there would be a fundamental distinction between real and apparent death. The former would be characterized by anarrest of the protoplasmic assimilationwhich is externally indicated by no sign. On the other hand, apparent death would be characterized bythe arrest of the formation and destruction of reserve-stuff. It would be externally manifested by two signs:—The suppression of material exchanges with the medium (respiration, alimentation) and the suppression of the functional acts (production of movement, of heat, of electricity, of glandular excretion).
Such would be the most expedient test for apparent or real death. The question occurs in the case of grains of corn in Egyptian tombs, and also of hibernating animals and reviviscent beings, and, in general, in the case of what has been called the state oflatent life. But from the practical point of view it is extremely difficult to apply this test and to decide if the phenomena which are arrested in the grain at maturity, in Leeuwenhoek’s tardigrada,[18]and in the dried-up Anguillulidæ[19]of Baker and Spallanzani, in the encysted colpoda[20]that a drop of warm water will revive, in the animals exposed by E. Yung and Pictet to a cold of more than a 100° C. below zero, are due to the general arrest of the two forms of assimilation, or to the arrest of the manufacture and utilization of reserve-stuff alone, or finally, to the arrest of protoplasmic assimilation alone. The latter, which is already very restricted in beings in a normal condition whose growth is terminated, may fall to the lowest degree in the being which, having no functional activity, is assimilating nothing. So that, to cut the question short, the experimenter who measures the value of the exchanges between the being and the medium has seldom to do more than decide between little and nothing. Hence his perplexity. But if experiment hesitates, theory affirms: it admitsa priorithat the movement of protoplasmic assimilation, an essential sign of vitality, is neither checked nor renewed, but proceeds continuously.
Is Nutrition, the Assimilating Synthesis, interrupted?—Nevertheless, there are many reasons for suspending all judgment as to this interpretation. It is questioned by most biologists. According to A. Gautier, the preserved grain of corn and the dried up rotifera are not really alive; they are like clocks in working order, ready to tell the time, but awaiting in absolute repose the first vibration which will set them going. As for the grain, it is the air, heat, andmoisture which supply the first impulse. In other words, the organization proper to the manifestation of life remains, but there is no life. The so-called arrested life is not a life.
It must be said, however, that the majority of physiologists refuse to accept this interpretation. They believe in an attenuation of the nutritive synthesis and not in its complete destruction. They think that this total suppression would be contrary to current ideas relative to the perpetuity of the protoplasm and the limited duration of the living element. The natural medium is variable, and even the mineral cannot remain eternally fixed. Still less is perennity a property of the living being. If ordinary life is for each individual of limited duration, the arrested life must also be of limited duration. We cannot believe that after an indefinitely prolonged sleep the grain of corn, or the paste-eel, or the colpoda, emerging from their torpor can resume their existence, like the Sleeping Beauty, at the point at which it was interrupted, and thus pass with a bound, as it were, through the centuries.
In fact the maintenance of the vitality of grains of corn from the Egyptian tombs and their aptitude to germinate after thousands of years are only fables or the result of imposture. Maspero, in a letter addressed to M. E. Griffon on the 15th July 1901, has clearly summed up the situation by saying that the grains of corn bought from the fellahs almost always germinate, but that this is never the case with those that the experimenter himself takes from the tombs.
To sum up, we must use the same language of nutrition and of life, of their uninterrupted progress,of their continuity, of their permanence, of their activity, and of their slackening. Living matter is always growing, much or little, slowly or quickly, in its reserve-stuff or in its protoplasm, for expenditure or accumulation. This inevitability of growth defines it, characterizes it, and sums up its activity. Development and the evolution of growth are consequences or aspects of nutrition.