The Chief Forms of Regulation
We have finished our long account of individual morphogenesis proper. If we look back upon the way we have traversed, and upon those topics in particular which have yielded us the most important general results, the material for the higher analysis which is to follow, it must strike us, I think, that all these results relate to regulations. In fact, it is “secondary” form-regulations, according to our terminology, that we have been studying under the names of equifinality, restitution of the second order, and so on, and our harmonious-equipotential systems have figured most largely in processes of secondary form-regulations also. But even where that has not been the case, as in the analysis of the potencies of the germ in development proper, form-regulations of the other type have been our subject, regulations of the primary or immanent kind, the connection of normal morphogenetic events being regulatory in itself. It was not, however, the phenomenon of organic regulation as such that afforded us the possibility of establishing our proof of the autonomy of morphogenesis: that possibility was afforded us by the analysis of the distribution of potencies; but upon this distribution regulation is based, and thus we may be said to have studied some types of regulation more or less indirectly when analysing potencies.
It therefore seems to me that we shall have hopes of a successful issue to our inquiries, if we now, on passing to what is called the physiology of the vegetative functions, proceed to focus our attention on the concept of regulation as such.
But let us first try to give a proper definition of our concept. We shall understand by “regulation” any occurrence or group of occurrences on a living organism which takes place after any disturbance of its organisation or normal functional state, and which leads to a reappearance of this organisation or this state, or at least to a certain approach thereto. Organisation is disturbed by any actual removal of parts; the functional state may be altered by any change among the parts of the organism on the one hand, by any change of the conditions of the medium on the other; for physiological functioning is in permanent interaction with the medium. It is a consequence of what we have said that any removal of parts also changes the functional state of the organism, but nevertheless organisation is more than a mere sum of reactions in functional life. All regulations of disturbances of organisation may be called restitutions, while to regulations of functional disturbances we shall apply the name adaptations. It is with adaptations that we have to deal in the following.
SPECIFIC ADAPTEDNESS NOT “ADAPTATION”
It is important to keep well in mind our definition of adaptation, as by doing so we shall be able to exclude at once from our materials a large group of phenomena which occasionally have been called adaptations, but which, in fact, are not of the adaptation type and therefore cannot be said to afford those problems which possibly might have been expected. Typical structures or peculiarities in functional life cannot be called “regulations” simply because they serve to maintain the life of their bearer. The mere existence of protective colours, forms of mimicry, etc., therefore, shows mere adaptedness, not “adaptation”. And if the organism selects specific amounts of specific kinds of organic food or of salts out of the combinations of salts or organic food normally offered to it in the medium, there cannot be said to occur a “regulation” or “adaptation” with regard to the permeability of the cell, nor is it strictly a case of “regulation”, if so-called selective qualities are discovered in the processes of secretion, say of the epithelium of the kidney.
All these facts are typical and specific peculiarities in form or functioning which are duly to be expected, where a very typical and specific organisation of the most elaborated kind exists. Indeed, after studying such an organisation we must not be astonished that functions in organisms follow lines which certainly they would not have taken without it. Take the fact which is quoted very often, that the migration of compounds or of ions in the organisms can happen quite contrary to all the laws of osmosis, from the less concentrated to the more concentrated side of a so-called “membrane”. There is no simple “membrane” in the organism, but a complicated organisation of an almost unknown character takes its place, and nothing, indeed, is against the assumption that this organisation may include factors which actually drive ions or compounds to the side of higher concentration, which indeed drive them by “doing work”, if we like to speak in terms of energy; and these factors included in organisation may very well be of a true physical or chemical nature.
In a more general form we now can sum up our discussion by saying: There never are adaptations where certain peculiarities of form are simply existing or where there are complications or even apparent deviations from the purely physico-chemical type of events which are, so to say, statical, i.e. fixed in quantity or quality, however peculiar or typically complicated they may be; all such peculiarities, indeed, may properly be called “adapted”, that is to say, very well fitted to perform a specific part in the service of normal general functioning, and they are “adapted” to their part by virtue of a certain “adaptedness” of the organisation; but they are not “adaptations” in the strict sense of the word.
PRIMARY AND SECONDARY ADAPTATIONS
We approach the subject of true adaptations, that is, of adapting processes, as soon as any kind of variation in form or functioning occurs which corresponds to a variation of any factor of the medium in the widest sense. But even here our work is by no means done by simply showing such a correspondence of outer and inner variations. We know very well already, from our former studies, that now we are faced by a further problem, that we are faced by the question whether we have to deal with simple primary kinds of adaptations or with the far more important secondary ones.
As the discrimination between primary and secondary regulations proves indeed to be of first-rate importance, you will allow me, I hope, to summarise our chief analytical statements regarding them in a most general form. We call primary regulatory any kind of morphogenetic or functional performance which, by its very intimate nature, always serves to keep the whole of organisation or of functions in its normal state. We call secondary regulations all features in the whole of morphogenesis or of functioning which serve to re-establish the normal state after disturbances along lines which are outside the realm of so-called normality. This analytical discrimination will help us very much to a proper understanding, though it will prove to be rather difficult in some cases clearly to separate primary adaptations from secondary ones on the one hand, and from mere adaptedness on the other.1
Morphological adaptation is a well-established fact, and I need only mention the striking differences between the land and water form of amphibious plants, or the differences between the same species of plants in the Alps and in the plains, or the very different aspect of the arms of an athlete and of an ascetic, to recall to your memory what is meant by this term.
Morphological adaptation is no part of individual morphogenesis proper, but occurs at the end of it; at least, it almost never occurs previous to the full individual life of an organism, previous to its true functional life; for it relates to the functions of the complete organism.
THE LIMITS OF THE CONCEPT OF MORPHOLOGICAL ADAPTATION
It is especially, though by no means exclusively, among plants that morphological adaptation assumes its most marked forms; and this topic, indeed, may very easily be understood if we remember that plant-life is in the very closest permanent dependence on the medium, and that this medium is liable to many changes and variations of all kinds. In order to elucidate our problem, it therefore seems convenient to restrict our considerations for a while to the study of plants. There exist very many external formative stimuli in the morphogenesis of vegetation: would it then be possible to regard every effect of such an external formative stimulus as a real morphological adaptation? No; for that would not meet the point. The general harmony of form is indeed concerned if gravity forces roots to shoot forth below at a spot where they can enter the ground, or if light induces branches and leaves to originate at places where they can obtain it for assimilation; but gravity and light themselves are mere formative stimuli—of the localising type—in these instances, for they relate only to the individual production of form, not to the functioning of already existing form. We therefore are warned not to confuse the effects of formative stimuli from without with real adaptive effects until we have fully analysed the particular case.
We have drawn a sharp line between causes and means of morphogenesis, applying the term “means” to those conditions of the morphogenetic process which relate neither to the specificity nor to the localisation of its constituents, though they are necessary for the accomplishment of the process in the most thorough manner. Would it be possible to connect our new concept of an adaptation with our well-established concept of a means of morphogenesis in such a way that we might speak of a morphological “adaptation” whenever any specific feature about morphogenesis proves to be immediately dependent for its success on some specific means, though it does not owe its localisation to that means as its “cause”? It seems to me that such a view would also fall wide of the mark. It is well known, for instance, that the flowers of many plants never fully develop in the dark; light is necessary for their morphogenesis. Is, therefore, their growth in the presence of light to be called a morphological “adaptation” to light? Certainly not: they simply cannot originate without light, because they require it for some reason. It is precisely here that our conception of light as a “means” of morphogenesis is most fully justified. There are many such cases; and there are still others of an apparently different type, but proving the same. All pathological forms produced in plants by animal parasites or by parasitic fungi could hardly be called adaptations, but must be attributed to some abnormality of means or of stimuli. It may be that the organism reacts as well as possible in these cases, and that if it reacted otherwise it would die—we know absolutely nothing about this question. But even then there would only be some sort of regulation in the process of pathological morphogenesis, but the process itself could hardly be called adaptive.
So far we have only learned what is not to be regarded as morphological adaptation. No response to external formative stimuli is in itself an example of adaptation, nor are processes dependent for their existence on any kind of condition or means to be called, simply because they are dependent on them, adaptations to those agents. What then, after all, is a morphological adaptation?
Let us remember what the word adaptation is really to mean in our discussions: a state of functioning is adapted—a state of functioning must therefore have been disturbed; but as functioning itself, at least in plants, certainly stands in close relations to the medium, it follows that all adaptations are in the last resort connected with those factors of the medium which affect functioning. In being correctives to the disturbances of functioning they become correctives to the disturbing factors themselves.
But again, the question seems to arise whether these factors of the medium, when they provoke an adaptation by some change that is followed by functional disturbance, do so in the capacity of “causes” or of “means”, and so if might seem that we have not gained very much so far by our analysis. The reproach, however, would not be quite justified, it seems to me: we indeed have gained a new sort of analytical concept, in the realm of causal concepts in general, by clearly stating the point that adaptations are related directly to functionality, and only indirectly, through functionality, to external changes. By the aid of this logical formulation we now are entitled to apply the term “cause”, in our restricted sense of the word, to every change of the medium which is followed by any sort of adaptation in regard to itself. Our definition stated that a “cause” is any one of the sum of necessary factors from without that accounts either for the localisation or for the specification of the effect, and the definition holds very well in this case. Indeed, the specification of the effect is determined by the outside factor in every case of an adaptation to it, by the mere fact of its being a specific adaptation to this specific factor.
We must not forget that in this chapter we are not studying real individual morphogenesis as the realisation of what has been inherited, but that at present we regard morphogenesis proper as an accomplished fact. Morphogenesis proper has laid the general lines of organisation; and now adaptation during the functional life, so to speak, imposes a second kind of organisation upon the first. It is for that reason that the meaning of the word “cause” is now becoming a little different from what it was before.
In order to study a little more in detail what has been discovered about morphological adaptation in animals and plants, let us separate our materials into two groups, one of them embracing adaptations with regard to functional changes from without, the other adaptations to those functional changes which come from the very nature of functioning.
ADAPTATIONS TO FUNCTIONAL CHANGES FROM WITHOUT2
The differences between plants grown in very dry air, very moist air, and water, respectively, are most distinctly seen in all the tissues that assist in what is called transpiration, that is, the exchange of water-vapour between the plant and the medium, but especially in the epidermis and the conductive fibres, both of which are much stronger in plants grown in the dry. Indeed, it seems from experiments that transpiration is the most essential factor to which “adaptation” occurs in amphibious plants, though the changes of the mechanical conditions according to the medium also seem to have some sort of structural effect. If plants stand very deeply in water, the conditions of illumination, so important for assimilation in plants, may have been altered, and therefore much of the structural change can be attributed also to them. It is unimportant in our general question what is due to one of these factors and what to the other. That there is a real sort of adaptation cannot be doubtful; and the same is true, as experimental observations of the last few years have shown, with regard to the structural differences between so-called sun-leaves and shade-leaves of plants grown in the air: it has been actually shown here that the functional life of the former goes on better in the sun, of the latter better in the shade.
It is very important to emphasise this point, as the adaptive character of all sorts of structural differences in plants dependent on light and on moisture has lately been denied, on the supposition that there is only a stopping of organogenesis in the case of the more simple, a continuance in the case of the more complicated modification, but nothing else. Indeed, all morphological adaptation has been conceived as only consisting in differences dependent upon the absence or the presence of necessary means or causes of development, and as offering no problem of its own. We have gained the right position from which to oppose this argument, it seems to me, in our formula that all adaptations do relate not directly to the agents of the medium, but to changes of functional states induced by those agents; that adaptations only are “adaptations” by being correctives to the functional state.
There simply is an “adaptation” of structure in such a sense in all the cases we have mentioned. We can say neither more nor less. Granted that one of the outside factors which comes into account is merely a necessary “means”: then why is the histological consequence of the presence of the means an actual adaptation to it as far as its relation to functioning is concerned; why is the consequence of its absence also an adaptation to this absence in its relation to functioning? Why, to complete the series, is the degree of the consequence of its presence an adaptation to the degree of its presence?
All these relationships, which are so many facts, have been absolutely overlooked by those who have been pleased to deny morphological adaptation to functional changes from without.
To do full justice to them, we may speak of “primary” regulative adaptations in all the cases mentioned above—applying the word “primary”, just as was done with regard to restitutions, to the fact that there is some sort of regulation in the normal connection of processes. We reserve the title of “secondary adaptations” for cases such as those described, for instance, by Vöchting,3 where not merely one and the same tissue originates adaptively with regard to the degree of its normal functioning, but where a profound disturbance of all functioning connections, due to the removal of portions of the organisation, is followed by histological changes at absolutely abnormal localities; that is, where a real change of the kind of functioning is the consequence of the adaptation. It, of course, will be found very difficult to discriminate such phenomena from real restitutions, though logically there exists a very sharp line between them.
TRUE FUNCTIONAL ADAPTATION4
But all other cases of morphological adaptation among animals, and several in the vegetable kingdom too, belong to our second group of these phenomena, which in our analytical discussion we have called adaptations to functional changes that result from the very nature of functioning, and which we shall now call by their ordinary name, “functional adaptations”.
It was Roux who first saw the importance of this kind of organic regulation and thought it well to give it a distinguishing name. By functioning the organisation of organic tissues becomes better adapted for functioning. These words describe better than any others what happens. It is well known that the muscles get stronger and stronger the more they are used, and that the same holds for glands, for connective tissue, etc. But in these cases only quantitative changes come into account. We meet with functional adaptations of a much more complicated and important kind, when for instance, as shown by Babak, the intestine of tadpoles changes enormously in length and thickness according as they receive animal or vegetable food, being nearly twice as long in the second case. Besides this, the so-called mechanical adaptations are of the greatest interest.
It has long been known, especially from the discoveries of Schwendener, Julius Wolff, and Roux, that all tissues whose function it is to resist mechanical pressure or mechanical tension possess a minute histological structure specially suitable to their requirements. This is most markedly exhibited in the stem of plants, in the tail of the dolphin, in the arrangements of the lime lamellae in all bones of vertebrates. All these structures, indeed, are such as an engineer would have made them who knew the sort of mechanical conditions they would be called upon to encounter. Of course all these sorts of mechanically adapted structures are far from being “mechanically explained”, as the verbal expression might perhaps be taken to indicate, and as indeed has sometimes been the opinion of uncritical authors. The structures exist for mechanics, not by it. And, on the other hand, all these structures, which we have called mechanically “adapted” ones, are far from being mechanical “adaptations”, in our meaning of the word, simply because they are “adapted”. Many of them indeed exist previous to any functioning; they are for the most part truly inherited, if for once we may make use of that ambiguous word.
But, the merely descriptive facts of mechanical adaptedness having been ascertained, there have now been discovered real processes of mechanical adaptations also. They occur among the statical tissues of plants, though not in that very high degree which sometimes has been assumed to exist; they also occur in a very high perfection in the connective tissue, in the muscles and in the bone tissue of vertebrates. Here indeed it has proved possible to change the specific structure of the tissue by changing the mechanical conditions which were to be withstood, and it is in cases of healing of broken bones that these phenomena have acquired a very great importance, both theoretically and practically: the new joints also, which may arise by force of circumstances, correspond mechanically to their newly created mechanical function.
We now, of course, have to ask ourselves if any more intimate analysis of these facts is possible, and indeed we easily discover that here also, as in the first of our groups of morphological adaptations, there are always single definite agents of the medium, which might be called “causes” or “means” of the adaptive effects, the word “medium” being taken as embracing everything that is external to the reacting cells. But of course also here the demonstration of single formative agents does not detract in the least from the adaptive character of the reaction itself. So we may say, perhaps, that localised pressure is the formative stimulus for the secretion of skeleton substance at a particular point of the bone tissue, or of the fibres of the connective tissue; the merely quantitative adaptations of muscles might even allow of a still more simple explanation. But adaptations remain adaptations in spite of that; even if they only deserve the name of “primary” regulations.
We have stated in the analytical introduction to this chapter and elsewhere, that functional changes, which lead to morphological adaptations of both of our groups, may arise not only from changes of factors in the medium, but also from a removal of parts. As such removal is generally followed by restitution also, it is clear that restitutions and adaptations very often may go hand-in-hand, as is most strikingly shown in a fine series of experiments carried out by Vöchting, which we have already alluded to. Here again I should like to lay the greatest stress upon the fact that, in spite of such actual connections, restitutions and adaptations may always be separated from one another theoretically, and that the former are never to be resolved into sums of the latter. Such a view has been advocated by some recent authors, especially by Klebs, Holmes, and Child:5 it is refuted, I think, by the simple fact that the first phase of every process of restitution, be it regeneration proper or be it a sort of harmonious differentiation, goes on without functioning at all, and only for future functioning.6
And there has been advocated still another view in order to amplify the sphere of adaptation: all individual morphogenesis, not only restitution, is adaptation, it has been said. In its strictest form such an opinion, of course, would simply be nonsense: even specific adaptive structures, such as those of bones, we have seen to originate in ontogeny previous to all specific functions, though for the help of them, to say nothing of the processes of the mere outlining of organisation during cleavage and gastrulation. But they are “inherited” adaptations, it has been answered to such objections. To this remark we shall reply in another chapter. It is enough to state at present that there is a certain kind of, so to speak, architectonic morphogenesis, both typical and restitutive, previous to specific functioning altogether.
If now we try to resume the most general results from the whole field of morphological adaptations, with the special purpose of obtaining new material for our further philosophical analysis, we have reluctantly to confess that, at present at least, it does not seem possible to gather any new real proof of life-autonomy, of “vitalism”, from these facts, though of course also no proof against it.
We have stated that there is, in every case of both our types of adaptive events, a correspondence between the degree of the factor to which adaptation occurs and the degree of the adaptive effect. We here may speak of an answering between cause and effect with regard to adaptation, and so perhaps it may seem as if the concept of an “answering reaction” (“Antwortsreaktion”), which has been introduced into science by Goltz,7 may come into account: but in our present cases “answering” only exists between a simple cause and a simple effect, and relates almost only to quantity and locality. There is therefore lacking the most important feature, which, as will be seen, would have made the new concept of value.
We only, I believe, can state the fact that there are relations between morphogenetic causes and effects which are adaptations, that functional disturbances or changes are followed by single histogenetic reactions from the organism, which are compensations of its disturbed or changed functional state. We are speaking of facts here, of very strange ones indeed. But I feel unable to formulate a real proof against all sorts of mechanism out of these facts: there might be a machine, to which all is due in a pre-established way. Of course we should hardly regard such a machine as very probable, after we have seen that it cannot exist in other fields of morphogenesis. But we are searching for a new and independent proof; and that is indeed not to be found here.
At present it must be taken as one of the fundamental facts of the organogenetic harmony, that the cells of functioning tissues do possess the faculty of reacting to factors which have changed the state of functioning in a way which normalises this state histologically. There is, however, one particular feature in all morphological adaptation, which, if further studied experimentally, might perhaps lead one day to a new and independent proof of vitalism.
It is a fact that all morphological adaptations start from cells which are not yet functioning but are in the so-called embryonic or indifferent condition.
This is a very important point in almost all morphological adaptation, whether corresponding to functional changes from without or resulting from the very nature of functioning. In fact, such cells as have already finished their histogenesis are, as a rule, only capable of changing their size adaptively, but are not able to divide into daughter-cells or to change their histological qualities fundamentally; in technical terms, they can only assist “hypertrophy” but not “hyperplasia”. Any adaptive change of a tissue, therefore, that implies an increase in the number of cellular elements or a real process of histogenesis, has to start from “indifferent” cells, that is to say, cells that are not yet functioning in the form that is typical of the tissue in question; and, strange to say, these “embryonic” cells—i.e. the “cambium” in higher plants and many kinds of cells in animals—can do what the functional state requires. We may speak of an adaptive equipotentiality of these cells. And this term is correct, even if the potencies of the indifferent cells relate only to histological types which are “normal” for the species in question.
It is but a step from morphological adaptations to adaptations in physiology proper. The only difference between regulations of the first type and those which occur in mere functioning is, that the resulting products of the regulation are of definite shape and therefore distinctly visible in the first case, while they are not distinctly visible as formed materials but are merely marked by changes in chemical or physical composition in the latter.
Metabolism, it must never be forgotten, is the general scheme within which all the processes of life in a given living organism go on; but metabolism means nothing else, at least if we use the word in its descriptive and unpretentious meaning, than change in the physical or chemical characteristics of the single constituents of that organism. In saying this, we affirm nothing about the physical or chemical nature of the actual processes leading to those physical or chemical characteristics, and by no means are these “processes” a priori regarded as being physical or chemical themselves: indeed, we have learned that in one large field, in the differentiation of our harmonious systems, they certainly are not. Now, if the metabolism does not end in any change of visible form, then true physiological processes, or more particularly physiological regulations, are going on before us. But we are dealing with morphogenetic events or regulations, if the result of metabolism is marked by any change in the constituents of form. This, however, may depend on rather secondary differences as to the nature of regulation itself, and any kind of metabolism may really be of the regulatory type, whether we actually see its result as a constituent of form, e.g. owing to the production of some insoluble compound, or whether we do not.
ON CERTAIN PRE-REQUISITES OF PHYSIOLOGICAL ADAPTATIONS IN GENERAL
We now must think of the general and important question, what types of adaptations may be expected in the field of physiology, and whether there may be certain classes of regulatory events which possibly might be expected to occur in the organism on a priori grounds, but which, nevertheless, are to be regarded as impossible after a more intimate analysis of its nature, even at the very beginning. Or, in other words, to what kinds of changes of the medium will an organism be found able or unable to adapt itself?
We know that the state of functioning must be altered in order to call forth any sort of adaptation at all. Now, there can be no doubt that a priori it would seem to be very useful for the organism, if it never would let enter into its blood, lymph, etc., be it through the skin or through the intestine, any chemical compound that would prove to be a poison afterwards. In fact, a man, judging on the principle of the general usefulness of all the phenomena of the living, might suppose that there would exist a sort of adaptation against all poisons to the extent that they would never be allowed to enter the real interior of the body. We know that such reasoning would be incorrect. But we also can understand, I suppose, that an a priori analysis of a more careful kind would have reasoned differently. How could the functional state of the organism be changed, and how, therefore, could adaptation be called forth by any factor of the medium which had not yet entered the organism, but was only about to enter it? Not at all, therefore, is such a regulation to be expected as we have sketched; if there is to be any adaptation to poisons, it only can occur after the poison has really acted in some way, and in this case we shall indeed find regulations.
Very often, indeed, the question has been raised by the defenders of a mechanistic theory of life: Why then did the organisms not reject all poisons from the very beginning? We may now simply reply—How could they do so? How could they “know” what is a poison and what is not, unless they had experienced it?—if we are allowed for a moment to use very anthropomorphistic language.
We repeat, therefore, that the functional conditions of the organism must have been actually changed in order that an adaptation may occur. Nothing is more essential to a clear understanding of our problems than to keep fully in mind the exact sense of this definition.
Two Meanings of the Word “Function”
But the word “function” seems to require a still further explanation.
This word is generally used with two different meanings, which we shall call, respectively, the proper function and the harmonious function. The proper function of any organic cell is that which it immediately performs; the pancreas cells, e.g., secrete trypsin. But the harmonious function is the effect of the performance of that cell upon the whole organism. The harmonious function of the pancreas cells, then, is to transform the food into substances which may be absorbed by the intestine and assimilated by the various tissues. The possibility of harmonious functioning rests upon the general “functional harmony” and the “harmony of constellation” of the organism (page 78).
Now we understand, so it seems to me, that that which starts adaptation is always a change in the totality of harmonious functioning, whilst the adaptation itself consists in a change of proper functioning. And this change occurs in such a way as to re-establish, more or less, the totality of harmonious functioning.
Some Particular Cases of Physiological Adaptation
If we now turn to particulars, we unfortunately see at once that, in wide areas of physiology, very many “adaptednesses” may be found, but very few real adaptations.
The so-called restoration of irritability in general and the regulation of temperature in warm-blooded animals may even be understood along physico-chemical lines.
As to the regulation of the permeability of cellular surfaces, serving the equilibrium of osmotic pressure, or the chemical composition of juices, or both, nothing has at present been established with absolute certainty. Almost every author has his own opinion about this subject, and I therefore omit all details.9
An “osmostat” seems to play a role here, just as in heat regulation a “thermostat”. This would signify mere adaptedness, the only true adaptation being realised, perhaps, in the fact that the osmostat adjusts itself by its own forces to a new equilibrium under abnormal conditions. But even this feature may be nothing but a primary regulation.
So-called adaptations of colour are mostly due to nervous influence, in the way of “seeing”, and, so far, do not belong to this chapter. If they are not, they probably rest upon a rather simple adaptedness.
The field of metabolism seems at the first glance to be really covered by adaptive regulations, but almost everything transpires to be pre-established, on the foundation of the given harmony of constellation and of functions in the adult organism.
In the state of fasting, however, there probably occurs a little more. In this state, oxydation, the necessary prerequisite of life, attacks the different tissues of the organism subjected to fasting in such an order that, after the combustion of the reserves, the most unimportant tissues with regard to life in general are destroyed first, the most important ones last. Thus in vertebrates, the nerve cells and the heart are preserved as long as possible; in infusoria it is the nucleus; in flatworms it is the nerve cells and the sexual cells which longest resist destruction, whilst almost all the rest of the organisation of these animals may disappear. I should not say that we can do very much with these facts at present in our theoretical discussion, but they are certainly witness of certain adaptive powers.
Some other adaptations have been discovered in fungi. Fungi are known to be satisfied with one single organic compound instead of the group of three—fat, carbohydrate, and albumen—necessary for animals. Now, Pfeffer showed that the most different and indeed very abnormal compounds were able to bring his subjects to a perfect growth and morphogenesis; and, moreover, he found that, if several kinds of such food were offered together, they were consumed quite indifferently as to their chemical constitution, but only with regard to their nutritive value: that sort of food which had produced a better growth than another when both were offered separately was found to save the latter from consumption whenever both were offered together.
Here we are faced by one of the most typical cases of regulations in metabolic physiology: the organism is able to decompose compounds of the most different constitution, which have never been offered to it before; but, nevertheless, it must remain an open question whether real “secondary” regulation has occurred, as nothing is known in detail about the single steps of metabolism in these fungi. There might be some ferments equally able to destroy different classes of compounds, and that the most nutritive compound is used up first may be a question of physico-chemical equilibrium.
That is almost all that is actually known of adaptation with regard to the use of an abnormal food supply. Though important, it cannot be said to be very much.
IMMUNITY THE ONLY TYPE OF A SECONDARY PHYSIOLOGICAL ADAPTATION
There is only one class of physiological processes in which the type of the secondary regulation is realised beyond any doubt. The discoveries of the last decades have proved that the so-called immunity against diseases is but one case out of numerous biological phenomena in which there is an adaptive correspondence between abnormal chemical stimuli and active chemical reactions on the part of the organism and in its interior, exceeding by far everything that was formerly supposed to be possible in physiological regulation.
The adaptive faculty of the organism against inorganic poisonous substances is but small comparatively, and is almost always due not to a real process of active regulation but to the action of substances pre-existing in the organism—that is, to a sort of adaptiveness but not adaptation.
It is in the fight against animal and vegetable poisons, such as those produced by bacteria, by some plants and by poisonous snakes, that the true adaptation of the organism reaches its most astonishing degree. The production of so-called “anti-bodies” in the body fluids is not the only means applied against noxious chemical substances of this kind: the existence of so-called histogenetic immunity is beyond all doubt, and Metschnikoff10 certainly was also right in stating that the cells of the organism themselves repel the attack of living bacteria. Cells of the connective tissue and the white blood cells, being attracted by them as well as by many other foreign bodies, take them in and kill them. This process, called “phagocytosis”, is of special frequency among lower animals, but it also contributes to what is called inflammation in higher ones.11 And there are still other kinds of defence against parasites, as for instance the horny or calcareous membranes employed to isolate trichinae and some kinds of bacteria. But all this is of almost secondary importance as compared with the adaptive faculties of the warm-blooded vertebrates, which produce anti-poisonous substances in their lymph and blood.
Discoveries of recent years have shown not only that against the “toxins” of bacteria, snakes, and some plants the organism is able actively to produce so-called “anti-toxins”—that is, soluble substances which react with the toxins and destroy their poisonous character—whenever required, but that against any foreign body of the albumen group a specific reaction may occur, resulting in the coagulation of that body. But the destruction of the noxious substance or foreign albumen actually present is not all that is accomplished by the organism. “Acquired immunity” proper, that is, security against the noxious material for a more or less extensive period of the future, depends on something more. Not only is there produced as much of the so-called “anti-body” as is necessary to combine with the noxious, or at least foreign, substances which are present, but more is produced than is necessary in the actual case. On this over-production depends all active immunity, whether natural or, as in some kinds of vaccination, artificial; and so-called “passive” immunity, obtained by the transfusion of the serum of an actively immune organism into another, also depends upon this feature.
This phenomenon in particular—the production of more of the antitoxin or the “precipitin” than is actually necessary—seems to render almost impossible any merely chemical theory of these facts. The reaction between toxin and antitoxin, albumen and precipitin, is indeed chemical—it may, in fact, be carried out in a test-tube; but whether the production of the anti-body itself is also chemical or not could hardly be ascertained without a careful and unbiassed analysis.
And, indeed, here if anywhere we have the biological phenomenon of adaptation in its clearest form. There are very abnormal changes of the functional state of the organism, and the organism is able to compensate these changes in their minutest detail in almost any case. The problem of the specification of the reactions leading to immunity seems to me, as far as I can judge as an outsider, to stand at present in the very forefront of the science. There cannot be the slightest doubt that especially against all sorts of foreign albumens the reaction is as strictly specific as possible; but there are some typical cases of specificity in the production of antitoxins also. It is, of course, the fact of specific correspondence between stimulus and reaction that gives to immunity its central position among all adaptations, no matter whether the old hypothesis of the production of specific anti-bodies proves tenable, or whether, as has been urged more recently by some authors, the anti-body is always the same but reacts differently according to the medium. In the latter case it would be the medium that is regulated in some way by the organism in order to attain a specific adaptedness.
NO GENERAL POSITIVE RESULT FROM THIS CHAPTER
But now let us look back to the sum of all the physiological reactions studied, and let us see if we have gained a new proof of the autonomy of life from our long chapter.
We freely admit we have not gained any really new proof, but we may claim, I think, to have gained some new indicia for the statement that the organism is not of the type of a machine, in which every single regulation is to be regarded as properly prepared and outlined.
It is precisely in the field of immunity that such a machinelike preparation of the adaptive effects seems almost impossible to be imagined. How indeed could there be a machine, the chemical constituents of which were such as to correspond adaptively to almost every requirement—to say nothing of the fact that the production of more of the protecting substance than is actually necessary could hardly be said to be “chemical”?
In fact, we are well entitled to say that we have reached here the very heart of life and of biology. If nevertheless we do not call the sum of our facts a real proof of vitalism, it is only because we feel unable to formulate the analysis of what happens in such a manner as to make a machine as the basis of all reactions absolutely unimaginable and unthinkable. There might be a true machine in the organism producing immunity with all its adaptations. We cannot disprove such a doctrine by demonstrating that it would lead to a real absurdity, as we did in our analysis of differentiation of form; there is only a very high degree of improbability in our present case. But an indirect proof must reduce to absurdity all the possibilities except one, in order to be a proof.
Mechanistic explanations in all branches of functional physiology proper, so much in vogue in the past, can indeed be said to have failed all along the line: the only advantage they have brought to science is the clearer statement of problems to which we are now accustomed. But we are not fully entitled to say that there never will be any mechanistic explanation of physiological functions in the future. It may seem as improbable as anything can be; but we wish to know not what is improbable but what is not possible.
Now, of course, you might answer me that after we have indeed shown that the production of form, as occurring on the basis of harmonious-equipotential systems, is a fact that proves vitalism, the acts taking place on the basis of that form after its production would have been proved to be vitalistic also, or at least to be in some connection with vitalistic phenomena. Certainly they would, and I myself, personally, should not hesitate to say so. But that is not the question. We have to ask: Is any new proof, independent of every other, to be obtained from the facts of physiological adaptation in themselves? And there is really none. Mere regulatory correspondence between stimuli and reactions, even if it be of the adaptive type and occur in almost indefinite forms, never really disproves a machine as its basis so long as the stimuli and reactions are simple and uniform. Later on, however, we shall see that vitalism may be proved by such a correspondence if the two corresponding factors are not simple and not uniform.
We must clearly see at this point what it really was in our analysis of differentiation that allowed us to extract a real proof of vitalism from it. Not the mere fact of regulability, but certain specific relations of space, of locality, lay at the very foundation of our proof. These relations, indeed, and only these relations, made it possible to reduce ad absurdum any possible existence of a machine as the actual basis of what we had studied. In our next chapter again it will be space relations, though analysed in a different manner, that will enable us to add a second real proof of vitalism to our first one.
With this chapter we conclude the study of organic regulation in all its forms, as far as morphogenesis and metabolism are in question.
But our analysis of these regulations would be incomplete, and indeed would be open to objections, if we did not devote at least a few words to two merely negative topics, which will be taken more fully into consideration later on.
A FEW REMARKS ON THE LIMITS OF REGULABILITY
There has never been found any sort of “experience” in regulations about morphogenesis or in adaptations of the proper physiological type. Nothing goes on “better” the second time than it did the first time;12 everything is either complete, whenever it occurs, or it does not occur at all.
That is the first of our important negative statements about regulations; the second relates to the phrase just used, “or it does not occur at all”. There are indeed limits of regulability; adaptations are not possible to every sort of change of the physiological state: sickness and death could not exist if they were; nor is restitution possible in all cases where it might be useful. It is a well-known fact that man is only able to heal wounds but is altogether destitute of the faculty of regeneration proper. But even lower animals may be without this faculty, as are the ctenophores and the nematodes for instance, and there is no sort of correspondence between the faculty of restitution and the place in the animal kingdom.
But no amount of negative instances can disprove an existing positive. Our analysis based upon the existence of regulations, therefore, is as little disparaged by cases where no regulability exists as optical studies are by the fact that they cannot be undertaken in absolute darkness.
Comp. Ungerer, Die Regulationen der Pflanzen, 2nd ed., 1926, a very valuable book. Ungerer proposes to reserve the name of “adaptation” for the secondary ones exclusively, and to call all other cases “adaptedness” or “harmony”.
Compare Herbst, Biol. Centralbl. 15, 1895; and Detto, Die Theorie der direkten Anpassung, Jena, 1904. A full account of the literature will be found in these papers.
Vöchting (Jahrb. wiss. Bot. 34, 1899) forced the bulbs of plants to become parts of the stem, and parts of the stem to form bulbs; in both cases the most characteristic changes in histology could be observed, being in part adaptations, but in part restitutions of the proper type. (See also my Organische Regulationen, 1901, p. 84.) A true and simple instance of a “secondary adaptation” seems to be furnished in a case described by Boirivant. In Robinia all the leaflets of a leaf-stalk were cut off: the leafstalk itself then changed its structure in order to assist assimilation, and also formed real stomata.
Roux, Gesammelte Abhandlungen, vol. i., 1895; in particular, Der Kampf der Telle im Organismus, Leipzig, 1881.
What has been really proved to exist by the very careful studies carried out by Child, is only certain cases of functional adaptation to mechanical conditions of the strictest kind, and relating to the general mobility only, but nothing more; such adaptations can be said to accompany restitution. See, for instance, Journ. Exp. Zool. 3, 1906, where Child has given a summary of his theory, and also his book Physiol. Foundations of Behaviour.
Even in Vöchting’s experiments (see page 126, note), in which adaptations are mixed with true restitutions in the closest possible manner, a few phenomena of the latter type could most clearly be separated. The stimulus which called them forth must have been one of the hypothetic sort alluded to in a former chapter (see page 81 f.). The best instances of true restitutions were offered in those cases, where, after the removal of all the bulbs, typical starch-storing cells were formed without the presence of any starch.
Beiträge zur Lehre von den Functionen der Nervencentren des Frosches, Berlin, 1869.
General literature: Fröhlich, Das natürliche Zweckmässigkeitsprincip in seiner Bedeutung für Krankheit und Heilung, 1894. Driesch, Die organischen Regulationen, 1901. A. Tschermak, “Das Anpassungsproblem in der Physiologie der Gegenwart,” in a collection of papers in honour of J. P. Pawlow, St. Petersburg, 1904. Bieganski, “Über die Zweckmässigkeit in den pathologischen Erscheinungen,” Annal. d. Naturphil. 5, 1906. Among the general text-books of physiology those by Pfeffer (Pflanzenphysiologie, 1897–1904) and von Bunge (Lehrbuch d. Phys. d. Menschen, 1901) are the fullest on the subject of “regulations”. See also different papers on general pathology by Ribbert.
For a fuller discussion compare the second German edition of this book (1921) and the paper of Fitting in Jahrb. wiss. Bot. 56.
Leçons sur la pathologic comparée de l’inflammation, Paris, 1892.
The other steps or phases in the process of inflammation have also been regarded as adaptive: the increased quantity of body fluid, for instance, is said to serve to dilute poisonous substances.
The few cases of an “improvement” of morphogenetic acts in hydroids described by myself are too isolated at present to be more than mere problems (Arch. Entw. Mech. 5, 1897). The same is true, it seems to me, with regard to certain discoveries made by R. Pearl on Ceratophyllum (Carnegie Inst. Wash. Publ. No. 58, 1907); and by Zeleny on a medusa (Jour. Exp. Zool. 5. 1907).