Part 1 — THE INDIVIDUAL ORGANISM WITH REGARD TO FORM AND METABOLISM (continued 3)
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We should only be repeating ourselves if we were to analyse again what happens here as the expression of the harmonious-equipotentiality itself. But indeed there occurs something new in this instance: the single mesenchyme cell not only has to perform in each case that single act of specific secretion which the case requires, but it also has to wander to the right place in order to perform it; there must be some order, not only about the acts of secretion after wandering, but also in the migrations themselves. If undisturbed ontogeny alone were possible, and if therefore a theory like that of Weismann were in place, we might say perhaps that each mesenchyme-cell is specified not only as to its performance in secretion, but also with regard to its chemotactical irritability, the latter being typically localised, so that its effect becomes typical, thanks to the typical arrangement of all the cells with respect to each other. But that is certainly not the case. Now, you may ask yourselves if you could imagine any sort of a machine, which consists of many parts, but not even of an absolutely fixed number, all of which are equal in their faculties, but all of which in each single case, in spite of their potential equality, not only produce together a certain typical totality, but also arrange themselves typically in order to produce this totality. We are indeed familiar with certain occurrences in nature where such curious facts are observed, but I doubt if you would speak of “machines” in these cases. The mesenchyme-cells, in fact, behave just as a number of workmen would do who are to construct, say, a bridge. All of them can do every single act, all of them also can assume every single position: the result always is to be a perfect bridge; and it is to be a perfect bridge even if some of the workmen become sick or are killed by an accident. The “prospective values” of the single workman change in such a case.
I well know that it is only an analogy which I am offering to you. The mesenchyme-cells have not “learned,” have no “experience.” All that is to occupy us next summer. But in spite of it, there is truth in the analogy; and perhaps you will prefer it to the merely abstract consideration.
ON CERTAIN COMBINED TYPES OF MORPHOGENETIC SYSTEMS
For the sake of completeness it may be remarked, only by the way, that the type of the proper harmonious-equipotential system may go hand in hand with another type of “systems” which play a part in morphogenesis; a type which we have shortly mentioned already and which will be studied fully a few chapters later. We know that there are equipotential systems with complex potencies: that is to say, systems which may produce a whole organism equally well from any one of their elements; we know the cambium of Phanerogams to be such a system. Now it is easily understood that the germ of our Echinus, say in the stage of two or four or eight cleavage cells, is not only an harmonious-equipotential system, but a complex-equipotential system too. Not only may there arise a whole organism out of 2/4 or 3/4; or 3/8, 4/8, 5/8, 6/8, 7/8 of its elements, in which cases the harmonious rôle of the single element with regard to its single performance in a totality is variable, but there may also arise four whole single larvae out of the four cells of the four-cell stage, or eight single whole larvae out of the eight-cell stage.67 In these cases, of course, each of the four or eight elements has performed not a part of the totality, changing with its “position,” but the totality itself. With respect to these possible performances the “systems” present in the four or eight-cell stages of cleavage must be called complex-equipotential ones.
We propose to give the name of mixed-equipotential systems to all those equipotential systems which, at the same time, may be regarded as belonging to the harmonious or to the complex type. It is not only among cleavage-stages that they are to be found; you may also find them very clearly exhibited in our ascidian Clavellina for instance. We know already that the branchial apparatus of this form is typically harmonious-equipotential, but it is complex-equipotential too, for it also may regenerate what is wanting in the proper way, by a budding from the wound; and the same is true of many other cases, the flatworm Planaria for instance.
Another type of systems, which might be said to be of a higher degree, is exhibited in some very strange phenomena of regeneration. It was first shown most clearly by some experiments of Godlewski’s that a whole tail may be regenerated from a wound inflicted on the body of a newt, even if this wound involves section of only a portion of the body-diameter. Section of the whole of the body-diameter of course would cause the formation of the whole tail also; but it was found that even an incomplete cross-section of the body is capable of performing the whole on a smaller scale. The series of possible cross-sections which are all capable of regeneration would have to be called a system of the complex type in this case; but, now we learn that every single cross-section is of the harmonious type, we must speak of complex-harmonious systems. What we have described is not the only instance of our new type of morphogenetic systems. Some other instances had been discovered a few years earlier, though nobody had pointed out their true significance. In the flatworm Planaria a partial cross-section is also capable of forming a whole structure, say a head, and all cases of so-called “super-regeneration” after the infliction of a complicated wound probably belong here also.
You may say that our two additions to the theory of systems are merely formal, and indeed I am prepared to concede that we shall not learn anything altogether new from their discussion: their analysis would lead either to what was our “first proof” of the autonomy of life-phenomena or to what will be our “second” one. But the mere descriptions of the facts discovered here will interest you, I think, and will fill your minds with more vivid pictures of the various aspects of form-autonomy.
While dealing with our harmonious-equipotential systems as the starting-points of processes of restitution, e.g. in Tubularia, Clavellina, the flatworms, and other instances, we always have regarded cross-sections of the body as constituting the elements of equipotentiality. Now cross-sections, of course, are by no means simple in themselves, but are made up of very different tissues, which are derivates of all three of the original germ layers—ectoderm, mesoderm, and endoderm. Owing to this composite character of the cross-sections, taken as elements of harmonious systems, a special phenomenon of morphogenesis is presented to us, which teaches somewhat more than the mere concept of harmonious-equipotentiality can express. If composite elements concerned in morphogenesis result in one whole organisation in spite of the development of the single tissues of these elements going on independently, then there must be a sort of correspondence or reciprocity of the harmonious development among these tissue constituents themselves; otherwise a proportionate form could not be the final result. We may conveniently speak of a reciprocity of harmony as existing between the single tissues or germ layers which constitute many harmonious-equipotential systems, and there can be little doubt that we have here an important feature with regard to general morphogenesis.68
A few other groups of morphogenetic facts may find their proper place here, though they are not properly to be regarded as additions to the theory of harmonious systems but as forming a sort of appendix to it.
THE “MORPHAESTHESIA” OF NOLL69
We may briefly mention that group of botanical phenomena, by which the botanist Noll has been led to the concept of what he calls “morphaesthesia,” or the “feeling” for form; a concept, the full discussion of which would lead to almost the same conclusions as our analysis of the harmonious systems has done. In the Siphoneae, a well-known order of marine algae with a very complicated organisation as to their exterior form, the protoplasm which contains the nuclei is in a constant state of circulation round the whole body, the latter not being divided by proper cell-walls. On account of this constant movement it is certainly impossible to refer morphogenetic localisation to definite performances of the nuclei. Nor can any sort of structure in the outer protoplasmic layer, which is fixed, be responsible for it, for there is no such structure there: hence there must be a sort of feeling on the part of the plant for its relative body localities, and on account of this feeling morphogenesis occurs. This “feeling” is styled “morphaesthesia” by Noll, and to it he tries to refer all sorts of different botanical form-phenomena,70 for instance what is called “autotropism,” that is, the fact that branches of plants always try to reassume their proper angle with regard to their orientation on the main axis, if this orientation has been disturbed. It may be an open question if this particular application of the theory is right: certainly there seems to be much truth in the establishment of the concept of morphaesthesia, and we only have to object to its psychological name. But that may be done in a more general form on a later occasion.
RESTITUTIONS OF THE SECOND ORDER
In the hydroid polyp Tubularia, already familiar to us as being a most typical representative of the harmonious-equipotential systems, a very interesting phenomenon has been discovered71, almost unparalleled at present but nevertheless of a general importance, a phenomenon that we may call a restitution of a restitution, or a restitution of the second order. You know that the first appearance of the new head of Tubularia, after an operation, consists in the formation of two rings of red lines, inside the stem, these rings being the primordia of the new tentacles. I removed the terminal ring by a second operation soon after it had arisen, disturbing in this way the process of restitution itself: and then the process of restitution itself became regulated. The organism indeed changed its course of morphogenesis, which was serving the purposes of a restitution, in order to attain its purpose in spite of the new disturbance which had occurred. For instance, it sometimes formed two rings out of the one that was left to it, or it behaved in a different way. As this difference of morphogenetic procedure is a problem by itself, to be discussed farther on, we shall postpone a fuller description of this case of a restitution of the second degree.
At present I do not see any way of proving independently the autonomy of life by a discussion of these phenomena; their analysis, I think, would again lead us to our problem of localisation and to nothing else; at least in such an exact form of reasoning as we demand.
ON THE “EQUIFINALITY” OF RESTITUTIONS72
I have told you already that Tubularia in the phenomena of the regulation of restitutions offers us a second problem of a great general importance, the problem of the Equifinality of Restitutions. There indeed may occur restitutions, starting from one and the same initial state and leading to one and the same end, but using very different means, following very different ways in the different individuals of one and the same species, taken from the same locality, or even colony.
Imagine that you have a piece of paper before you and wish to sketch a landscape. After drawing for some time you notice that you have miscalculated the scale with regard to the size of the paper, and that it will not be possible to bring upon the paper the whole of the landscape you want. What then can you do? You either may finish what you have begun to draw, and may afterwards carefully join a new piece of paper to the original one and use that for the rest of the drawing; or you may rub out all you have drawn and begin drawing to a new scale; or lastly, instead of continuing as you began, or erasing altogether, you may compromise as best you can by drawing here, and erasing there, and so you may complete the sketch by changing a little, according to your fancy, the proportions as they exist in nature.
This is precisely analogous to the behaviour of our Tubularia. Tubularia also may behave in three different ways, if, as I described to you, the terminal one of its two newly arisen rings of tentacle primordia is removed again. It may complete what is left, say the basal tentacle ring, then put forth from the horny skeleton (the “perisarc”) the new head as far as it is ready, and finally complete this head by a regular process of budding regeneration. But it also may behave differently. It may “erase” by a process of retro-differentiation all that has been left of what had already been formed, and then may form de novo the totality of the primordia of a new head. Or, lastly, it may remove a part of the middle of the one ring of tentacle rudiments which was left, and may use this one ring for the formation of two, which, of course, will not be quite in the normal relations of place with regard to each other and to the whole, but will be regulated afterwards by processes of growth. Thus, indeed, there is a sort of equifinality of restitution: one starting-point, one end, but three different means and ways.
It would, of course, contradict the principle of univocality, as we shall see more fully later on, to assume that there actually are different ways of regulation whilst all the conditions and stimuli are the same. We are obliged to assume, on the contrary, that this is not the case, that there are certain differences in the constellation, say of the general conditions of age or of metabolism, which are responsible for any given individual choosing one process of restitution instead of another; but even then the phenomenon of equifinality remains very striking.
It has long been known that restitution in general does not always follow the same lines of morphogenesis as are taken by ontogeny, and it was this feature that once led Roux to point out that the adult forms of organisms seem to be more constant than their modes of origin. But, comparing ontogeny with restitution in general, we see that only the ends are the same, not the points of starting; the latter are normal or non-typical in ontogeny, atypical in restitution. In the new discoveries of an equifinality of restitutions we have the same starting-point, which is decidedly non-typical but atypical, i.e. dependent on our arbitrary choice, leading by different ways always to the same end.
There may be many who will regard the fact of equifinality as a proof of vitalism. I should not like to argue in this easy way; I indeed prefer to include part of the phenomena of equifinality in our first proof of autonomy, and part in the second one, which is to follow.
Another important phenomenon of the equifinality of regulation was discovered by Morgan. A species of the flatworm Planaria was found to restore its totality out of small pieces either by regeneration proper, if the pieces were fed, or by a sort of rearrangement of material, on the basis of its harmonious-equipotentiality, if they were kept fasting. It is important to note that here we see one of the conditions determining the choice of the way to restoration, as we also do in the well-known equifinal restitutions of the root in plants, where the behaviour of the organism depends on the distance of the operation-wound from the tip.73 In Tubularia the actual stage of restitution that has been already reached by the stem when the second operation takes place, may account for the specification of its future organogenesis, but this is not at all clearly ascertained at present.
Clavellina also shows equifinality in its restitution, as has already been shortly mentioned. The isolated branchial apparatus may restitute itself by retro-differentiation to an indifferent stage followed by renovation; or it may regenerate the intestine-sac in the proper way. Nothing is known here about the conditions, except perhaps that young individuals seem more apt to follow the first of these two ways, older ones the second; but there are exceptions to this rule.
The discussion of other instances of equifinality, though important in themselves, would not disclose anything fundamentally new, and so we may close the subject with the remark that nothing can show better than the fact of the equifinality of restitutions how absolutely inadequate all our scientific conceptions are when confronted with the actual phenomena of life itself. By analysis we have found differences of potencies, according as they are simple or complex; by analysis we have found differences of “systems,” differences of means, and indeed we were glad to be able to formulate these differences as strictly as possible: but now we see how, in defiance of our discriminations, one and the same species of animals behaves now like one sort of our “systems,” and now like the other; how it uses now one sort of “potencies,” now another.
But even if it is granted that, in the presence of such phenomena of life, our endeavour seems to be like a child’s play on the shores of the ocean, I do not see any other way for us to go, so long, at least, as our goal is human science—that is, a study of facts as demanded by our mental organisation.
REMARKS ON “RETRO-DIFFERENTIATION”
We shall finish this part of our studies by mentioning a little more explicitly one fundamental fact which has already entered incidentally into our considerations, viz. retro- or back-differentiation.74 We know that it occurs in Clavellina and in Tubularia; we may add that it also happens in Hydra, and that in the flatworm Planaria the pharynx, if it is too large for a piece that is cut out, may be differentiated back and be replaced by a new pharynx, which is smaller.
It is not death and sloughing of parts that occurs in these cases,75 but a real process of active morphogenesis; not, however, a process consisting in the production of visible manifoldness, but the opposite. Loeb was the first to lay much stress upon this topic, and indeed, there may appear a very strange problem in its wake: the problem, whether all morphogenesis might be capable perhaps of going backwards under certain conditions.
It is important to note that in most76 cases retro-differentiation occurs in the service of restitution: it goes on wherever restitution requires it. This fact alone would show that not very much could be explained here by the discovery of modern chemistry, important as it is, that one and the same “ferment” or “enzyme” may affect both the composition and the decomposition of the same compound. We could regard what is called “catalysis” solely as an agent in the service of entelechy. But this point also will become clearer in another part of the work.
C. ADAPTATION
Introductory Remarks on Regulations in General
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, back-differentiation, 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 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. And that is what we shall do: on our way through the whole field of physiology, we shall always stop at any occurrence that has any sort of regulatory aspect, and shall always ask ourselves what this feature has to teach us.
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.
Let us begin our studies of adaptations in a field which may justly be called a connecting link between morphogenesis and physiology proper, not yet wholly separated from the science of the organic form, morphology.
1. Morphological Adaptation
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 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 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 many77 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 it 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. Almost all of our previous general considerations have applied to the former group, with which we shall now proceed to deal.
ADAPTATIONS TO FUNCTIONAL CHANGES FROM WITHOUT78
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,79 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.
A few more concrete instances may now close this account of adaptation to functional changes coming from without. Though almost all the adaptive characters in the aquatic forms of amphibious plants represent a less complicated state of organisation than the corresponding structures in their terrestrial forms, and therefore have wrongly been regarded as simply due to a stopping of morphogenesis for want of necessary means, yet there are a few of them that are positive complications in comparison with the land-forms: the so-called aërenchyme, especially well developed in the water-form of Jussiaea is such an instance. This tissue stands in the direct service of respiration, which is more difficult to be accomplished under water than ordinarily, and represents a true adaptation to the altered function.
Among animals there is only one well-studied instance of our first type of adaptive morphological characters. Salamandra atra, the black salamander, a species which only inhabits regions at least two thousand feet above sea-level, does not bring forth its young until metamorphosis has taken place. The larvae, however, may be removed from the mother’s body at an earlier stage and forced to complete their development in water. Under these circumstances, as was shown in an excellent memoir by Kammerer,80 they will change the whole histological type of their gills and skin in order to meet the new functional conditions. The change of the conditions of functioning is very severe here, for whereas the gills had served for nutrition and respiration in the uterus—by a process of endosmosis—they now serve for respiration only, and, of course, are surrounded by quite an abnormal chemical medium.
TRUE FUNCTIONAL ADAPTATION81
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 adaptation.”
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 Babák,82 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 mechanical processes of 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.
So far a short review of the facts of “functionelle Anpassung.” They seem to prove that there does exist a morphological adaptation to functional changes which result from the very nature of functioning. In fact, the actual state of all functioning tissue, the intensity of its state of existence, if you care to say so, may be said to be due to the functioning itself: the so-called atrophy by inactivity being only one extreme of a very long line of correspondences.83
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.84 But adaptations remain adaptations in spite of that; even if they only deserve the name of “primary” regulations.
THEORETICAL CONCLUSIONS
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 always have been separated from another theoretically, and that the forms 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:85 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.86
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 was introduced into science by Goltz87 and which is to play a great part in our discussions of next summer, 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.88
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. And it is a fact also that even cells, which are not yet functioning but are in the so-called embryonic or indifferent condition contributing to the physiological completion of the tissue, react to factors embracing new functional conditions of the whole in a manner which leads to an adaptation of that whole to those conditions.
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. It is to be hoped that future investigations will lay a greater stress upon this very important feature of all adaptation.
2. Physiological Adaptation89
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.
I do not mean to say that these are the only differences between mere physiological activities or regulations and organogenesis proper, as an originating of typical form-combination; but if we regard, as we do in this chapter, the given organisation of a living being as a substratum of its functional life, morphological and physiological adaptations are indeed of almost the same logical order.
We had best therefore begin our discussions with a recapitulation of our problem. We are studying adaptations in functioning—that means we want to know how the organism behaves with regard to any change which may take place in its functional state. We apply the term regulation, or in particular adaptation, to any kind of reaction on the part of the organism which re-establishes the normal state of functioning, and we now want to learn to what degree such adaptations exist in the field of physiology.
SPECIFIC ADAPTEDNESS NOT “ADAPTATION”
It is important to keep well in mind our strictly formulated theme, 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 regulations by physiological authors, 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 peculiarities in functional life cannot be called “regulations” for this very reason. If, for instance, 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, as indeed is most typically shown for instance by the roots of plants, 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 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.90
I lay great stress upon these statements, as I should like to be as careful as possible in the admission of anything like a “proof” of vitalism. It was want of scientific criticism and rigid logic that discredited the old vitalism; we must render our work as difficult as possible to ourselves, we must hold the so-called “machine theory” of life as long as possible, we must hold it until we are really forced to give it up.
In a more general form we now can sum up our discussion by saying: There never are adaptations in physiology, requiring any special analysis, where there are only 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 any sense of the word.
PRIMARY AND SECONDARY ADAPTATIONS IN PHYSIOLOGY
We approach the subject of true adaptations, that is, of adapting processes, as soon as any kind of variation in 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 of physiology. But before we turn to apply our definitions to actual facts, another preliminary problem has to be solved.
ON CERTAIN PRE-REQUISITES OF ADAPTATIONS IN GENERAL
We are thinking 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.
You may perhaps regard this discussion as a little too academical and hair-splitting, but here again it was for the sake of ensuring a perfectly sound foundation of our chief principles that I undertook it. 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 now may reply to that only—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.
ON CERTAIN GROUPS OF PRIMARY PHYSIOLOGICAL ADAPTATIONS
General Remarks on Irritability.—Turning now to more special groups of problems concerning physiological adaptations, let us begin with the primary class of them, and let us first say a few words on a subject which occasionally has been regarded as the basis of physiological regulation in general. I refer to a most important fact in the general physiology of irritability. Irritability of any kind is known to be re-established, after it has been disturbed by the process of reacting to the stimulus, and in certain cases, in which two different—or rather two opposite—kinds of reactions are possible on the same substratum, which increase with regard to one process whilst decreasing at the same time with regard to the other. The irritability of the muscle or of the leaves of Mimosa is a very good instance of the first case, whilst the second more complicated one cannot be illustrated better than by what all experience has taught us about the irritability of the retina. The retina is more irritable by green rays and less by red ones the more it has been stimulated by the latter, and more sensitive to light in general the more it has been exposed to darkness; and something very similar is true, for instance, as regards phototactic irritability in plants, all these phenomena being in relation to the so-called law of Weber.91
It seems to me that there would be little difficulty in harmonising the phenomenon of the inversion of irritability with the so-called principle of the “action of masses” and with the laws of certain “reversible” processes well known in chemistry. As to the simple fact of the re-establishment of irritability after stimulation has occurred, or, in certain other cases, the fact that in spite of permanent stimulation irritability seems to exist permanently also, physical analogies or even explanations might very well be found.92
If now we ask whether there is anything like an adaptation appearing in the general characteristics of irritation and irritability, it seems to me that we may answer the question in an affirmative manner, as far as primary regulation comes into account. We, certainly, have not studied any abnormal regulatory lines of general functioning, we only have studied general functioning itself; but, indeed, there was a certain sort of regulation in functioning. Of course, by showing that one of the most general features of all functioning is primary-regulatory in itself, we do not deny the possibility of many specific functions in which real secondary regulations actually do exist. Nothing indeed is asserted about the specific character of functioning in its different types, by proving that one of the general features of all functioning may comparatively easily be understood. It seems to me that this important logical point has not always received the attention it deserved.
The Regulation of Heat Production.93—Having finished our introductory remarks we now turn to the proper study of special physiological functioning with regard to its adaptive side, and begin with the most simple cases.
The so-called “regulation of heat” in warm-blooded vertebrates is an instance of a special function which can be said to be regulatory in itself. There exists a normal blood heat for each species, which is maintained no matter whether the temperature of the medium rise or fall. It might seem at first as if in this case there were a little more of an adaptive regulation than only its well-known primary type; no reversion, one might say, of the direction of one and the same process occurs in the regulation of heat production, but one kind of process is called into action if it is necessary to raise the temperature, and another whenever it is necessary to lower it. Even in the dilatation and constriction of capillary vessels there are different nerves serving for each operation respectively, and far more important are the increasing of transpiration for cooling, the increasing of combustion for heating—two radically different processes. But, nevertheless, there is a certain unity in these processes, in so far as a specific locality of the brain has been proved to be the “centre” of them all; it is to this centre of course that the analysis of heat production considered as a kind of regulation or adaptation must be directed. Such an ultimate analysis, it seems to me, would have to classify heat regulation under the primary type of adaptations in physiology without any restriction. The centre acts in one sense or in the other, if stimulated by any temperature beyond a very limited range, and it is in the action of the centre that the “regulation” of heat consists.94
Primary Regulations in the Transport of Materials and Certain Phenomena of Osmotic Pressure.—Very similar phenomena of regulation are present in many processes concerned in the whole of metabolism. Let us consider for a moment the migration of materials in plants. Whenever any compound is used at a certain place, a permanent afflux of this compound to that place sets in from all possible directions. No doubt this is a “regulation,” but it is also the function itself, and besides that, a very simple function based almost entirely on well-known laws of physical chemistry. And in other cases, as in the ascent of water to the highest tops of our trees, which purely physical forces are said to be insufficient to explain, we can appeal to the unknown organisation of many cells, and there is nothing to prevent our attributing to these cells certain functions which are, if you like to say so, regulatory in themselves. Among other facts of so-called regulations there is the stopping of metabolic processes by an accumulation of their products: as, for instance, the transformation of starch into sugar is stopped, if the sugar is not carried away. Of course that is a regulation, but it again is an intrinsic one, and it is one of the characteristics of reversible chemical processes to be stopped in that way. I know very well that in this particular case a certain complication is added by the fact that it is a so-called ferment, the diastase, which promotes the transformation of starch into cane-sugar, and that this ferment is actively produced by the organism: but even its production would not prove that any real kind of secondary regulation exists here, if nothing more were known about such an active production than this single case.
In a special series of experiments almost all carried out in Wilhelm Pfeffer’s botanical laboratory at Leipzig, an attempt has been made to discover in what manner the cells of plants are able to withstand very high abnormalities of the osmotic pressure of the medium—that is to say, very great changes in the amount of its salinity. That many, particularly the lower plants, are able to stand such changes had been ascertained already by the careful examinations of Eschenhagen; but recent years have given us a more profound insight into what happens. Von Mayenburg95 has found that sundry of the species of Aspergillus, the common mould, are able to live in very highly concentrated solutions of several salts (KNO3 and Na2SO4). They were found to regulate their osmotic pressure not by taking in the salts themselves, but by raising the osmotic pressure of their own cell sap, producing a certain amount of osmotically active substances, probably carbohydrates. If in this case it were possible to assume that the osmotic pressure of the medium were the real stimulus for the production of the osmotic substances in the cell, stimulus and production both corresponding in their degree, we should be entitled to speak of a primary though physiological96 regulation only; and it seems to me that despite the discoveries of Nathansohn that certain algae and cells of higher plants are able to change the permeability of their surfaces in a way which regulates the distribution of single salts or ions in the sap of their cells without any regard to pure osmotic equilibrium, such a simple explanation might be possible.97
There are many regulation phenomena connected with osmotic pressure and permeability in animal physiology also, though at present they are not worked out as fully as possible. The works of Frédéricq, J. Loeb, Overton and Sumner98 would have to be taken into account by any one who wished to enter more deeply into these problems. We can only mention here that permeability to water itself also plays its part, and that, according to Overton’s experiments, it is a kind of solubility of the media in the very substance of the cell surface on which all permeability and its regulation depend.
Chromatic Regulations in Algae.—The phenomena of osmotic pressure and its regulation may be said to be the preliminaries of metabolism proper, conditions necessary for it to take place. Now there is another branch of such preliminaries to metabolism, in which the most interesting regulation phenomena have been lately discovered. It is well known that what is called assimilation in plants, that is, the formation of organic compounds out of carbon dioxide (CO2) and water, occurs only in the light by means of certain pigments. This pigment is in all higher plants and in many others the green chlorophyll, but it may be different in certain species of algae, and can generally be said99 to be of the colour complementary to the colour of those rays which especially are to be absorbed and to be used for assimilation. But here we have “adaptedness,” not adaptation. It was in some species of primitive algae, the Oscillariae, that Gaidukow100 found a very interesting instance of an active regulation in the formation of pigments. These algae always assume a colour which corresponds to the accidental colour of the rays of the medium and is complementary to it; they become green in red light, yellow in blue light, and so on—that is, they always actively take that sort of colouring which is the most suitable to the actual case.101 There indeed occurs a sort of complementary photography in these algae; but, though adaptive, it could hardly be said to exceed the limits of “primary phenomena.”
Metabolic Regulations.—And now we enter the field of regulations in metabolism itself. There are two kinds of outside factors of fundamental importance for all metabolic processes: food is one, and oxygen is the other. And metabolism as a whole is of two different aspects also: it both serves for assimilation proper—that is, building up—and it supplies the energy for driving the functional machine. It is clear that food alone—together of course with the assimilating means of the organism, can account for the first type of metabolism, while both food and oxygen, or some sort of substitute for the latter, as in certain bacteria, supply functional energy. Of course we are not entitled to say that the importance of so-called oxidation or respiration is exhausted by its energetic rôle: it certainly is not, for if it were, the organism would only be stopped in its functions if deprived of oxygen but would not die. It seems that certain substances always arise in the metabolism, in the processes of decomposition, which have to be burnt up in order not to become poisonous. But we shall return to the phenomena of organic oxidation in another chapter of the book, and shall deal with them from a more general point of view.102
Let us now try to take a short survey of all the regulations discovered relating to the substitution of one kind of food for another. We have said that food serves in the first place as building material, in the second place as fuel. It only deserves brief mention that, as all recent investigations have shown, fats, carbohydrates, and albumen are equally well able to serve as fuel.103
It is in the state of fasting, i.e. in the case of a real absence of all nourishing materials, that the organism has proved to be capable of regulations of the most marked nature, with regard to the combustion of its own materials. Respiration, we know, must go on if death is to be avoided, and now indeed it has been found that this process 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, as the very careful studies of E. Schultz104 have lately shown, 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 very astonishing adaptive powers.105
We now turn to study the cases of a compensation of nourishments serving for the real building up of the organism. Albumen, we know, is absolutely indispensable for animals, even for adults, though nothing is known about the purpose it serves in the latter; its place can be taken of course by those less complicated compounds which result from its first decomposition, effected by pepsin and trypsin, but nothing else will do. The salts of sea-water, according to Herbst’s experiments, may only vary to a very small degree if the development of marine animals is to go on well; potassium may be replaced by caesium or rubidium, and that is all. Much the same is true of the salts necessary to plants. It will not surprise us very much to hear that algae can also be successfully fed with the potassium salts of organic compounds, and higher plants with acid amides or glucoses instead of carbonic acid, as those products are normal steps in their assimilation; and it may also be fairly easily understood that nitrogen can be offered in organic form instead of as a nitrate.
It was in the group of fungi that really important adaptations with regard to the proper form-producing alimentation were first discovered, and these are of a very complicated kind indeed. 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,106 and that the most nutritive compound is used up first may be a question of physico-chemical equilibrium.
That is almost all107 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. But could we expect very numerous regulations here at all after what we laid down in a former paragraph about the possibilities of adaptive regulation in general? The functional state must have been altered in order that such regulations may occur. Now there is no doubt that this state may be really altered only if an abnormal food has first been taken in altogether by the cell-protoplasm of the body-surfaces, but never if it has only entered the cavity of the intestine, which, strictly speaking, is a part of the exterior medium. Fungi indeed not only take in the abnormal food, but also know what to do with it, but all animals are obliged to treat first with their chemical secretions what happens to be present in their intestine, in order that it may be taken up by their living cells, and one hardly can wonder that these secretions are only formed in correspondence to a limited number of outside stimuli. In fact, as soon as we look upon what adaptive or regulatory work happens in metabolism inside the body interior, we meet, even in animals, regulations of a far more developed type.
Discoveries of the last few years have taught us that almost all metabolic processes in the organism, including oxidation, are carried out by the aid of special materials, the so-called enzymes or ferments. These are known to exist in the most different forms even in the inorganic world. They are simply chemical compounds, of specific types, that bring about chemical reactions between two other chemical materials, which in their absence would either not go on at all or would go on very slowly. We cannot enter here into the much disputed chemical theory of what is called “catalysis”: we can only say that there is no objection to our regarding almost all metabolic processes inside the organism as due to the intervention of ferments or catalytic materials, and that the only difference between inorganic and organic ferments is the very complicated character of the latter and the very high degree of their specification.
Such a statement, of course, does not say that all metabolism has proved to be of a chemical nature: the action of the ferment when produced is chemical, but we do not know at all how the ferment is produced; we only know that a high degree of active regulation is shown in this production. In fact, it has been proved in some cases, and probably will be proved in a great many more in the near future, that all metabolic ferments, whether they promote oxidation or assimilation proper or chemical decomposition, are produced in a regulatory manner with regard to the specific compound to be dissociated or to be built up. In this way the whole field of metabolism is really covered by “regulations.” Are they real “secondary” ones? Of course the regulatory correspondence applies to the process of secretion in the first place, not to the actual formation of the ferment inside the cell. The correspondence as to secretion, no doubt, is of the primary type; is there any secondary regulation with regard to the real production of the ferment? I am sorry that I cannot answer this question affirmatively. Nothing is known at present, even here, that really proves the existence of adaptation of the secondary type: there might be a sort of statical “harmony” at the base of it all, established before all functioning for functioning.108
The only facts of secondary metabolic regulations which are known at present have been found in combination with phenomena of restitution after real disturbances of organisation, where, indeed, numbers and numbers of regulatory changes of metabolism, both in animals and plants, have also been recorded. But there is not one case of a secondary regulation really known to affect pure metabolism alone.109 This is a new indicium of the primacy of form in the organism.
IMMUNITY THE ONLY TYPE OF A SECONDARY PHYSIOLOGICAL ADAPTATION
There is only one class of physiological processes in which the type of the real secondary regulation occurs. The discoveries of the last twenty years have proved beyond all doubt, and future discoveries will probably prove even more conclusively, 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 organic regulation.
The adaptive faculty of the organism against inorganic poisonous substances110 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. Metallic poisons, for instance, may be transformed into harmless compounds by being combined with albumen or sulphuric acid and thus becoming insoluble, or free acids may be neutralised, and so on; but all these processes go on to a certain extent only, and, as was mentioned already, are almost always the result of reactions with pre-existing materials. Only in a few cases is there any sort of true adaptation to metallic substances, such as sublimate and, in a very small degree, arsenic, comparable in some respects with the adaptation to abnormally high temperatures. The organism which has been accustomed to receive at first very small amounts, say, of sublimate, and then receives greater and greater amounts of this substance by degrees, will at the end of this treatment be able to stand a quantity of the poison that would have been instantly fatal if administered at the first dose.111 But the explanation of this adaptation is not known in any case; there seems to be some similarity between it and the so-called histogenetic immunity against organic poisons.
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 Metschnikoff112 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.113 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.
It is impossible to say here114 more than a few words about the phenomena and the theory of immunity proper, which have attained the dimensions of a separate science. Let me only mark those general points which are of the greatest theoretical interest. Discoveries of the most 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.115
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. There can be no doubt that the well-known theory of Ehrlich,116 the so-called theory of side-chains (“Seitenkettentheorie”) has given a great impulse to the progress of science; but even this theory, irrespective of its admissibility in general, is not a real chemical one: the concept of a regeneration of its so-called haptophore groups is a strictly biological concept.117
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 many 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 machine-like 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 twenty years ago, 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 say118 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. Next summer, 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 most 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;119 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. It is not altogether impossible that there may be found, some day, certain conditions under which every organism is capable of restoring any missing part; but at present we know absolutely nothing about such conditions.120
But no amount of negative instances can disprove an existing positive—which is what we have been studying. Our analysis based upon the existence of regulations 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.
D. INHERITANCE: SECOND PROOF OF THE AUTONOMY OF LIFE
All organisms are endowed with the faculty of re-creating their own initial form of existence.
In words similar to these Alexander Goette, it seems to me, has given the shortest and the best expression of the fact of inheritance. Indeed, if the initial form in all its essentials is re-created, it follows from the principle of univocality, that, ceteris paribus, it will behave again as it did when last it existed.
By the fact of inheritance life becomes a rhythmic phenomenon, that is to say, a phenomenon, or better, a chain of phenomena, whose single links reappear at constant intervals, if the outer conditions are not changed.
The Material Continuity in Inheritance
It was first stated by Gustav Jaeger and afterwards worked out into a regular theory by Weismann, that there is a continuity of material underlying inheritance. Taken in its literal meaning this statement is obviously self-evident, though none the less important on that account. For as all life is manifested on bodies, that is on matter, and as the development of all offspring starts from parts of the parent bodies, that is from the matter or material of the parents, it follows that in some sense there is a sort of continuity of material as long as there is life—at least in the forms we know of. The theory of the continuity of “germ-plasm” therefore would be true, even if germ-cells were produced by any and every part of the organism. That, as we know, is not actually the case: germ-cells, at least in the higher animals and in plants, are produced at certain specific localities of the organism only, and it is with regard to this fact that the so-called theory of the “continuity of germ-plasm” acquires its narrower and proper sense. There are distinct and specific lines of cell-lineage in ontogenesis, so the theory states, along which the continuity of germ-protoplasm is kept up, which, in other words, lead from one egg to the other, whilst almost all other lines of cell-lineage end in “somatic” cells, which are doomed to death. What has been stated here is a fact in many cases of descriptive embryology, though it can hardly be said to be more than that. We know already, from our analytical and experimental study of morphogenesis, that Weismann himself had to add a number of subsidiary hypotheses to his original theory to account for the mere facts of regeneration proper and the so-called vegetative reproduction in plants and in some animals, and we have learned that newly discovered facts necessitate still more appendixes to the original theory. In spite of that, I regard it as very important that the fact of the continuity of some material as one of the foundations of inheritance has clearly been stated, even if the specialised form of the theory, as advocated by Weismann in the doctrine of the “germ-lineages” (“Keimbahnen”) should prove unable to stand against the facts.
The important problem now presents itself: What is the material, the matter, which is handed down from generation to generation as the basis of inheritance? Weismann, as we know, regarded it as a very complicated structure, part of which by its disintegration became the foundation of individual embryology. We have disproved, on the authority of many facts, the latter part of this assumption; but of course the first part of it may turn out to be true in spite of this. We have no means at present to enable us to say a priori anything positive or negative about the important question of the nature of that matter, the continuity of which in inheritance is in some sense a self-evident fact, and we therefore shall postpone the answer until a later point of our analytical discussion.
On Certain Theories which Seek to Compare Inheritance to Memory
It will be advisable first to study some other theoretical views which have been put forward with regard to inheritance. The physiologist Hering, as early as 1876, compared all heredity to the well-known fact of memory, assuming, so to say, a sort of remembrance of all that has happened to the species in the continuity of its generations; and several German authors, especially Semon, have lately made this hypothesis the basis of more detailed speculation.
It is not clear, either from Hering’s paper121 or from Semon’s book,122 what is really to be understood here by the word “memory,” and, of course, there might be understood by it very different things, according to the author’s psychological point of view. If he is a “parallelist” with regard to so-called psychical phenomena, he would use the word memory only as a sort of collective term to signify a resultant effect of many single mechanical events, as far as the material world of his parallel system comes into account, with which of course the problem of inheritance alone deals; but if he maintains the theory of so-called psycho-physical interaction, the psychical would be to him a primary factor in nature, and so also would memory. As we have said, it is by no means clear in what sense the word “memory” is used by our authors, and therefore the most important point about the matter in question must remain in dubio.
But another topic is even more clear in the theory of inheritance, as stated in Hering’s and Semon’s writings. The hypothetical fact that so-called “acquired characters” are inherited is undoubtedly the chief assumption of that theory. Indeed, it would be difficult to understand the advantage of the ambiguous word memory, had it not to call attention to the hypothetic fact that the organism possesses the faculty of “remembering” what once has happened to it or what it once has “done,” so to speak, and profiting by this remembering in the next generation. The zoologist Pauly indeed has stated this view of the matter in very distinct and clear terms.
As we soon shall have another occasion to deal with the much-discussed problem of the “inheritance of acquired characters,” we at present need only say a few words about the “memory-theory” as a supposed “explanation” of heredity. Undoubtedly this theory postulates, either avowedly or by half-unconscious implication, that all the single processes in individual morphogenesis are the outcome either of adaptations of the morphological type, which happened to be necessary in some former generation, or of so-called contingent “variations,” of some sort or other, which also happened once in the ancestral line. Such a postulate, of course, is identical with what is generally called the theory of descent in any of its different forms. This theory is to occupy us in the next lectures; at present we only analyse the “memory-theory” as a theory of heredity in itself. In any case, to regard memory as the leading point in inheritance, at least if it is to signify what is called memory in any system of psychology, would be to postulate that either adaptation or contingent “variation” has been the origin of every morphogenetic process. Indeed, the American physiologist Jennings did not hesitate to defend such a view most strongly, and many others seem to be inclined to do the same.
But such an assumption most certainly cannot be true.
It cannot be true, because there are many phenomena in morphogenesis, notably all the phenomena akin to restitution of form, which occur in absolute perfection even the very first time they happen. These processes, for the simple reason of their primary perfection, cannot be due either to “learning” from a single adaptation, or to accidental variation. We shall afterwards employ a similar kind of argument to refute certain theories of evolution. It therefore may be of a certain logical interest to notice that at present, combating the memory-theory of inheritance, and hereafter, combating certain theories of descent, we select not “adaptation” or “variation” as the central points to be refuted, but the assumed contingency of both of them.
The word “memory,” therefore, may be applied to the phenomena of inheritance only in a very figurative meaning, if at all. We do not wholly deny the possibility of an inheritance of acquired characters, as will be seen later on, and to such a fact there might perhaps be applied such a term as “memory” in its real sense, but we simply know that there is something in inheritance which has no similarity whatever to what is called “memory” in any species of psychology. A primary perfection of processes occurring quite abnormally proves that there is a “knowing” of something—if we may say so—but does not prove at all that there is a “remembering.”