Physiological Foundations of Behavior

Even if it is true that these different forms of spatial pattern are independent or largely so of the specific differences of different protoplasms, the kinds of organs and parts which appear in the pattern must depend more or less upon the specific differences. The apical end of a plant axis, for example, develops as a growing tip, the apical end of a hydra as a mouth region surrounded by a ring of tentacles. Again, in bilateral forms the anterior end may be a growing tip, as in Marchantia, a head, as in bilateral animals (Fig. 1). In other axes also, the working out of the pattern differs in different protoplasms. Evidently then, organisms with the same general plan may be very different in actual structure because the materials, the protoplasms, are different.

The general spatial pattern also constitutes the basis on which the relations of dominance and subordination characteristic of the particular organism develop. In the spherically symmetrical pattern there is no fixed dominance, except in so far as such a relation may arise between surface and interior. In the cell, for example, the nucleus appears to dominate the cytoplasm in certain respects, while in others it is probable that the cytoplasm, or some part of it, dominates the nucleus. Undoubtedly these relations are, In part at least, transportative or chemical, but whether a transmissive factor is concerned, we do not know. As regards the different parts of the surface there is no fixed dominance. Differential excitation may determine the dominance, now of one part, now of another.

The axiate pattern differs from this in constituting a basis for definite and fixed relations of dominance and subordination, though their range and degree may vary widely according to conditions. In the axiate plant the growing tip dominates the axis, and in the animal an apical region or head, containing the chief aggregation of nervous tissue represents the primary dominant region. The symmetry pattern also determines certain minor relations of dominance and subordination, e. g., between peripheral and central in radiate forms, and between dorsal, lateral and ventral in bilateral forms. The complication of axiate pattern in the symmetrical ani-

mals, and particularly in the vertebrates, brings with it complica- _ tions in the relations of dominance and subordination, and in higher vertebrates and man the nervous relations have become almost in- - conceivably complex. But whatever the differences in the working out of the details of pattern in different protoplasms, the general spatial pattern as expressed in polarity and symmetry, and the pattern of physiological relation, as expressed in the relation of dominance and subordination, are indissociable. In fact, as will appear, the evidence indicates that they are different aspects of the same general factor which constitutes the basis of organismic pattern in protoplasm.

From the viewpoint of this chapter, the general features of organismic pattern must be clearly distinguished from the specific morphological and physiological characteristics of individual organisms. These latter represent the working out of an organismic pattern in a specific protoplasm as material. Organismic pattern in general stands in somewhat the same relation to the individual organism as the plan of a house does to a particular house. The individual house represents the plan worked out in certain materials. Organismic pattern is what distinguishes an organism from other things. But the particular kind of organism depends not merely upon the presence of an organismic pattern but upon the specific protoplasm in which the pattern is worked out.

In the case of physiological polarity, for example, whatever we may conceive its nature to be, we believe that it is essentially similar in different organisms. If then we discover what polarity is in one sort of organisms we are justified in concluding that polarity in other organisms is similar in nature. But in each kind of organism the polarity exists in a specific protoplasm and this protoplasm determines how the polarity pattern shall work out in each particular case. The polarity does not determine whether an axiate plant or an axiate animal, or whether a particular species of plant or animal, shall arise: it merely determines a physiological axis along which the differentiations determined by the hereditary potentialities of the particular protoplasm occur.

The pattern is first of all a factor in the physiology of development, 7. ¢., in the realization of hereditary potentialities of the particular protoplasm in which it exists. Something determines which potentialities shall be realized in each particular region of the developing organism and this something is the organismic pattern. For example, in certain liverworts, as well as various other plants, every cell is potentially able to give rise to a new growing tip and so to a whole new individual, but normally only a certain cell develops as a growing tip and the others perform other functions in an orderly way. Again in Planaria and various other animals, every level of the body is potentially capable of giving rise to a head, but in the normal animal the head arises only from certain cells at one end of the axis. The potentialities are given in the hereditary constitution of the protoplasm and are realized as the organismic pattern determines.

_ In short, the facts indicate that the specific constitutions of particular protoplasms are not the only nor the primary factors in determining the origin of the individual organism as a physiological order and integration appearing in a protoplasmic substratum. Un- questionably the constitution of the particular protoplasm determines the kind or species of individual which develops, but the real question is whether this constitution alone does or can determine that an organism shall arise. In other words, is not an organism the result of a reaction of a protoplasm to environment, and since all protoplasms give rise to organisms is not this reaction fundamentally non-specific with respect to the constitutions of particular protoplasms? An attempt to answer this question is reserved for later chapters.

In the preceding chapter it was pointed out that the fundamental physiological characteristic of organismic pattern is a relation of dominance and subordination established by physiological correlation between parts. Physiological integration takes place on a basis of dominance and subordination or control and being controlled. Some _ further consideration of the various mechanisms of integration and In physiological integration of the organism two sorts of factors are evidently concerned: differences in physiological condition or constitution in different regions or parts, 7. ¢., specialization or differentiation, and physiological correlation of one sort or another between parts. The existence of definite and orderly physiological correlation between parts depends of course on the existence of definite and orderly physiological differences in the parts concerned, however such differences may have arisen. These two factors, then, physiological differences in and physiological correlation erweee parts constitute “the organism as a whole.’’ Given the pattern of the individual organism, the mechanisms which make it behave as a whole are the mechanisms of physiological correlation. The problem of the organism as a whole is the problem of the origin, development and maintenance of the mechanisms of integration in their relation to origin, development and maintenance of the individual. This is first of all a problem of physiology, not of heredity, because as we have seen, heredity does not account for the individual, but merely for the potentialities some of which are realized in the individual.

At the risk of some repetition it seems necessary to emphasize once more the point developed in Chap. II (pp. 8-10), that the organism represents, not simply the integration which constitutes life, but an integration of living systems which differ in some way from each other, 7. ¢., an integration of different rates or kinds of living. To determine how these different sorts of life differ from each other, how the differences arise, how they are localized as different regions or parts of the organism and how they determine physiological correlation, this is to determine what the organism as a whole is.

The assertion that organismic pattern is a pattern on a larger scale than that of protoplasm (pp. 4, 8-12) is simply an assertion of this fact, that the organism is an integration of living protoplasms rather than merely the sort of integration which constitutes life. Physiological correlation in the proper sense then comprises all the physiological relations between the different living protoplasms and their products which make up the parts, organs, tissues, etc., of an organism. It obviously constitutes relation of higher order of magnitude than the relations between the components of a single protoplasmic system.

However we define life and wherever we draw the line between living and non-living, it remains true that an organism as an individual represents an integration into an orderly whole of ways of living, differing either quantitatively or qualitatively from each other. These different ways of living are given as hereditary potentialities in the so-called germ plasm out of which the individual develops, and each organism represents in its various parts the realization of certain of them. As soon as differences or parts appear, physiological correlation between them becomes possible and constitutes the mechanism of integration.

Like the relations between living protoplasm and its external environment (see pp. 12-17) the physiological relations between the different protoplasmic systems, parts, organs, etc., of an organism are either material, involving primarily the mass transportation of substance, or dynamic, involving primarily the transfer of energy. We must learn something of the forms in which these two groups of correlative factors appear in the organism and of their réles in the process of organismic integration,

Material correlation includes all those relations between parts in which the essential feature is the transportation in mass of a substance or substances from one to the other or others, The manner in which the transportation occurs may differ widely in different cases, but this is a matter of detail. For example, a substance may be - transported passively in solution or in suspension in a moving fluid _ within the body as in the case of salts, sugar, fats, etc., in the blood of animals and to some extent salts and sugar in the sap of plants. Again simple osmotic factors or more commonly the more complex condition commonly known as semi-permeability may be concerned - in transportation. It is by no means necessary to assume that the substance always remains unchanged during transport. It may undergo electrolytic, dissociation or association, or it may enter chemical reaction, in fact, transportation in many cases may consist in the passage of a chemical group from molecule to molecule in a certain direction. But whatever the method of transport the essential characteristic of material correlation is that the effect produced is in some way associated with the physivo-chemical constitution of the substance transferred. Certain substances may produce at least some of their correlative effects through certain generic characteristics which they share with many other substances: for example, electrolytes and their ions may produce correlative effects of electrolytic or ionic character quite apart from their chemical constitution; CO) as well as many other substances may produce effects through change in the hydrogen-ion concentration. Various substances may alter surface tension, water content, colloidal dispersion, etc., and so bring about correlative effects in a generic rather than in a specific

In many other cases there is a greater degree of specificity in material or transportative correlation, and the effect produced is apparently in some way related to the chemical constitution of the substance transported. The products of the glands of internal secretion, e. g., the thyroid, the adrenals, etc., are commonly regarded as examples of this sort of transportative correlation, 7. @., so-called chemical correlation. Such substances known or postulated are now often called hormones, 7. ¢., substances which arouse, activate, or set in motion something, viz., a physiological process. The researches of recent years have shown that chemical correlation of this specific sort is of very great importance and complexity in the higher animals and man, and some physiologists have been inclined to regard it as the fundamental factor in physiological integration. Sach’s theory of formative substances and its later modifications in the hands of Loeb, Morgan, Conklin and others are essentially theories of physiological integration which either assert or imply the fundamental importance of chemical correlation in embryonic or regulatory devel-

opment. Ritter (19, Chaps. XVIII—XX) is also inclined to regard material correlation as the primary factor in organismic integration. Concerning the importance in physiological integration of material or transportative correlation in general and of those forms of it commonly called chemical correlation there can be no possible doubt. In general the specificity and complexity of this sort of correlation undoubtedly increase with the increase in number and specialization of different organs and tissues, and are therefore greatest in the higher animals and man. Many facts also indicate that the specificity and complexity of chemical correlation increase in the course of individual development. It is not difficult to understand how this comes about: increase in degree and complexity of specialization of organs and tissues means a more highly specific chemical constitution of each; with this is associated more highly specific metabolic reactions and products; and finally these factors must be concerned in determining a higher degree of specificity of chemical correlation between organs and parts of the highly specialized species or stages. These facts in themselves are highly significant with respect to the réle of transportative correlation in physiological integration. They show clearly enough that transportative correlation depends first of all upon the existence of differences of some sort in the parts concerned. If we conceive the organism as a physicochemical system we cannot doubt that specific chemical correlation between certain parts depends upon the existence of specific differences in those parts. The specific substance transported must be Fic. 10.—Diagram illustrating Produced in one or certain of them and

the basis of transportative corproduce certain effects in others. Morerelation. Specific transportative > if thi - : . correlation between the different VEY, if this sort of correlation is orderly regions (A-E) or between any and definite in character as it is in organtwo of them, is possible only ; th i ; é after specific differences have Ms, the differences on which it depends arisen between the regions conmust be orderly and definite. Such difcerned. en

, ferences cannot originate through transportation of a substance because if al] parts are alike all will produce the same substances in the same amounts. To illustrate by a simple diagram (Fig. 10), transportative correlation exists between A on the one hand and B and C on the other. A must be different from B and C: it must represent to some extent a different organ or tissue. Simi- _ larly if transportative correlations exist between B and E and between

C and D all four of these regions must be different from each other in some way, otherwise definite relations would be impossible. Moreover, as noted above, transportative correlation as we find it in the organism differs in order of magnitude from the physico-chemical relations between molecules or chemical groups which constitute life in a protoplasmic system. It is not merely the process of living in such a system but it is a material relation between different protoplasmic, cellular or multicellular systems in which the process of living is different in some way (pp. 8-12).

It is clear then that transportative correlation cannot exist until the different systems are present, that is to say until the organismic pattern has appeared, therefore it cannot originate such pattern. The flow in opposite directions of stem-forming and root-forming substances postulated by Sachs for plants cannot occur autonomously, but becomes possible only when regional differences of some sort are present which determine such flow. Such differences may conceivably _ be either inherent, or determined by external conditions, but in any case they are more fundamental factors than the hypothetical substances in determining the pattern of the plant. The segregation of substances in the animal egg, or along the axis of the animal organism must be determined by preéxisting differences of some sort in the different regions. Hormone relations between parts are possible only when the parts are already different. There is in fact no escape from ~ the conclusion that transportative correlation as a material correlation between living systems cannot of itself originate organismic pattern, but is itself a consequence of the existence of such pattern. The basis of that pattern must be some factor, either inherent or external, which is able to determine in an orderly and definite way in a protoplasm, a cell, or a cell mass the regional differences in the rate or kind of the processes of living on which material correlation depends. Only through the origin of such regional quantitative or qualitative differences can an actual organism arise, and transportative correlation in the organism is an incident and consequence of the fundamental organismic pattern.

Dynamic correlation involves primarily the transfer or transmission of energy rather than the mass transport of material. Transport of ions or of electrons from one molecule or atom to another must of course occur in various forms of dynamic correlation, but such transport differs in process and effect from the mass transport of substances. In dynamic correlation the essential factor is the energy, while in material correlation it is the particular substance. Of course various substances transported in the body serve as sources of energy, but the energy is liberated in these cases through chemical reaction after they have been transported to certain parts of the body, while dynamic correlation is initiated by an energy change and this change is then transmitted in one way or another.

Dynamic correlation in the organism is accomplished chiefly in two ways: through the direct mechanical transmission by pressure or tension of mechanical changes; and through the transmission of excitation. Of course transmission or conduction of other forms of energy, heat, light, electricity, may occur in living protoplasms, and be of some correlative significance. The conduction of heat, for example, is important in maintaining and regulating body-temperature. The transmission of light through the refractive apparatus of the eye makes vision possible. Conduction of electricity is probably occurring in all living organisms at all times. But the chief importance of these forms of energy as correlative factors lies in their relation to excitation and its transmission. All forms of energy may bring about excitation in living protoplasm and the chief significance to the organism of all except mechanical energy is as excitatory agents, 7. e., as factors initiating energy changes of definite character in the living system. It is true, therefore, even though transmission or conduction of any form of energy may occur in protoplasms, that dynamic correlation in the organism is chiefly either mechanical or excitatory and transmissive in character.

Mechanical and transmissive correlation.—Purely mechanical correlation consists in pressure and tension. In such correlation the source of the energy involved is wholly external to the part affected. This behaves as inert body in accordance with the laws of mechanics. For example, in development change of shape of a part may be brought about mechanically by the pressure of other parts upon it, or by tension of growth. Again, movements of parts by means of muscles represent primarily mechanical correlation. Mechanical correlation, as the term is used here, means merely the mechanical factor in physiological correlation. Any mechanical correlation may have nonmechanical, as well as mechanical effects. - The effects of pressure and tension on living parts are not purely mechanical, but may include changes in the protoplasmic system itself. Nevertheless, the purely mechanical factors constitute so definite a feature of correlation and

- are so widely different from the factors of excitation and transmission that the distinction is useful. Excitation and transmission differ from mechanical correlation in that they involve reversible or partly reversible changes in the energy relations between components of the protoplasmic system. Since all protoplasms are highly complex physico-chemical systems in which the various changes are closely interrelated, alteration of the energy relations of the system results in general, either in excitation, an acceleration, or in inhibition, a retardation of living. In these changes the external factor merely initiates and the result is determined primarily by the energy relations within the protoplasm, not by the energy of the external factor. For present purposes excitation rather than inhibition is of primary importance.

All living protoplasms are irritable or excitable to some degree, both by various extra-protoplasmic dynamic factors and by the dynamic factor concerned in excitation of an adjoining protoplasmic region. The excitation of one protoplasmic region by another in continuity with it constitutes physiological transmission of excitation. Undoubtedly the changes which constitute excitation differ to some extent in different protoplasms and perhaps in the same protoplasm under different conditions. The relations between chemical reactions, e. g., the oxidations, and physical changes in excitation may differ widely in different protoplasms, and it is not at all improbable that the primary change which brings about excitation differs in different protoplasms or even in the same protoplasm with different exciting factors. But in spite of such differences it is clear that excitation in general involves acceleration in certain changes which liberate energy in living systems, and in a broad sense it may be regarded as an accelleration of livnig. Excitation rather than inhibition is important in correlation because from what has been said it appears that so far as known inhibition is not transmitted as such. The existence of inhibitory nervous correlation is of course a familiar fact, but in such cases the inhibitory effect is apparently produced, not by transmission of an inhibitory change, but by transmission of an excitation and the mechanism of the final inhibitory effect is still obscure.

Dynamic correlation in relation to organismic pattern. — As regards the part played by dynamic correlation in physiological integration, it is evident at once that transmission of excitation is far more important than purely mechanical correlation. Mechanical correlation may be a factor in determining shape and position of various parts, and as already pointed out, it is an essential feature in motor reactions, but it is evident that a definite and orderly mechanical correlation, such as we find in organisms, is dependent upon the existence of definite and orderly organismic pattern in which differences of mechanical condition exist at different points. In the function of motor organs generally, from cilia and flagella to the complex musculoskeletal systems of the higher animals, mechanical correlation is an essential factor, but the correlation is a result of the pattern and has nothing to do with its origin. Again, mechanical relations of pressure and tension may affect growth and differentiation, though their action in such cases is not directly mechanical, but rather a matter of excitation or inhibition. The internal structure of bone, the direction of connective tissue fibers in tendons, apparently also the differentiation of muscle, if Carey’s conclusions are correct (Carey, ’20, ’21), are determined by reactions of living protoplasm to relations of pressure and tension and similar reactions are undoubtedly concerned in many other differentiations. In these cases, as in purely mechanical correlation, the mechanical relations which determine the growth and differentiation are themselves determined by the organismic pattern. The mechanical relations of differential growth are possible only when different parts have been determined and are growing in an orderly way. In short, mechanical correlation though obviously a factor of great importance in motor behavior, and also concerned in growth and differentiation is, like material or transportative correlation, a secondary factor in organismic integration.

It remains to determine whether the other form of dynamic correlation, the transmission of excitation, will throw any further light upon the problem of physiological integration. In the first place attention was called above to the fact that all living protoplasms are to some extent excitable by external factors and capable of transmission of such excitation. Although the processes of excitation and transmission may differ in details in different protoplasms, excitation and transmission are, generically speaking, non-specific in the sense that they occur in some form in all protoplasms independently of their differences in constitution. Second, the only pattern necessary for the occurrence of excitation and transmission is the pattern of a protoplasm with a limiting surface in contact with environment. Preéxisting physiological axes and differentiation. of different regions are entirely unessential. Excitation is primarily a reaction of a living protoplasm to an external dynamic factor:‘and transmissive correlation is the excitation of one protoplasmic region

by another. . In other words, the regional physiological differences which make transmissive correlation possible arise through the local action of an external factor. If we imagine a living protoplasmic system without any regional pattern of organismic magnitude except a limiting surface, which is merely that part of the protoplasm in contact with the external world and completely reversible, it is ee that local excitation of such a system at any point such as

A (Fig. 11) introduces a differential not previously present. The region A as an excited region excites adjoining regions and transmission occurs to B and C, and if the decrement is not too steep, to D and EF or still further. The presence or absence, or the steepness of decrement in the degree or the intensity of the excitatory change in the course of transmission depends upon the constitution of the particular protoplasm concerned. \4 It is apparently true, however, that in most if not in all protoplasms in which 2 specialized conducting paths are not present, such a decrement appears, so that the range of effectiveness of transmission is limited. In such a primitive transmission process points at different distances (B and D,’or C and E, Fig. 11) from the point A of the origin of the excitation will show different Fic. 11—Diagram_ illustrating

5 the basis of transmissive correladegrees of excitatory change, decreastion. For the occurrence of transing from A toa point at a greater or missive correlation preéxistent difless distance from A at which it ceases ere ee Exciter to be effective in producing further tion of some point (A) determines oe hie the differential which initiates transmission. The result of the exjancomission. citation at A is then an excitationtransmission gradient of greater or less length, the different levels of which represent different degrees or intensities of excitation.