Physiological Foundations of Behavior

been a fundamental factor in making organisms what they are. It has been effective in two ways, physiologically, through the changes in protoplasm determined by excitation in the individual, and indirectly through the evolution of excitability, the process and mechanisms of excitation and transmission, and the integration of such” mechanisms. The ability of protoplasms to bring about excitation in their environment is biologically significant chiefly in relation to other organisms. Man of course is able with the aid of various tools to make fire, to bring about explosions, electrical excitation and various other excitatory changes in non-living systems, and these are of great though not of fundamental significance for human life. But in the relations of organisms to each other the excitatory factor has be-_ come always more significant during the course of evolution. In the higher animals and man the excitatory factor is unquestionably the primary factor in relations between individuals, the material factor being significant only as it is excitatory in effect. In fact all social integration is based upon the excitatory relation. By this is meant merely that the actions concerned in such integration are primarily determined and ordered by the energy impacts upon the sense organs of the individual. In the case of man speech and the written word are the most important means of communication and integration, but their action on the individua! is accomplished through the excitability of his protoplasm. All his relations with other individuals, whether they involve material exchange, 7. e€., in social terms, commerce, or communication by speech, writing, signal, or symbol of any kind, are based upon the excitatory relation. The significance of this fact in social integration will be considered in later chapters (Chaps. XVI, XVII).

It has already been noted that the material relations between protoplasm and the external world are in general specific and qualita- _ tive in character, involving different substances, though of course different quantities, 7. e., rates, degrees, amounts of material exchange, are possible. The dynamic or excitatory relations are, however, fundamentally non-specific or quantitative, involving energy transfer as the primary factor rather than mass exchange of substances. This difference is, as will appear, of fundamental significance for the - conception of the individual organism as a physiological order and integration. Protoplasm must have originated in specific material relations between different physico-chemical systems and unquestionably the present specific hereditary constitution of any particular protoplasm must be primarily dependent upon the whole history of its material relations with the external world.

On the other hand, all protoplasms exist as individual organisms and as regards the more general features the pattern of the organism shows no relation to specific protoplasmic constitution. For example, cells composed of very different protoplasms are almost or quite indistinguishably alike in form and general structure and the organ- - ismic axial relations, polarity and symmetry are very similar in many different protoplasms. When we regard the individual organism from this viewpoint it appears as primarily a non-specific or quantitative dynamic order in a specific protoplasm. In other words, cA ganismic pattern is primarily a non-specific dynamic pattern in a specific protoplasm. Apparently such a pattern can originate only 4 in the non-specific dynamic relations between protoplasms and environment. To what extent this conclusion is supported by facts, later chapters will show. /

That the organism represents a unity and order of some sort is believed by most biologists, but widely different conceptions and interpretations of this unity and order have been advanced and their ~ existence has sometimes been ignored. Much of the discussion of the organism as a whole has suffered from a lack of clearness concerning the nature of the “wholeness.” It seems to be clear enough, however, that this wholeness is the unity and order evident in the individual organism from the beginning of development through all

its life in all its various aspects. This unity and order are associated with the specialization and differentiation of parts in definite and orderly ways and with the resulting physiological relations between them (see Chap. V), but in all these processes unity and order are clearly apparent. The problem of the wholeness of the organism is then the problem of the origin and nature of the unity and order of the individual. (Cf. Ritter, ’19.) The various conceptions of the organism fall naturally into several groups and the brief consideration of these in the present chapter will serve not only to indicate the position of this problem in biological theory but also to clear the ground for the presentation of evidence in foilowing chapters.

The idea has been widespread among biologists that an elementary or fundamental organism of some sort exists and that all more complex organisms consist of groupings or associations according to some plan of these elementary organisms. But opinions differ widely as to what constitutes the elementary organisms. From the physiological viewpoint the cell or protoplast is commonly regarded as the elementary organism (Verworn, O. Hertwig), but the morphological theorists of the descriptive period in z0dlogy have postulated elementary organisms of various sorts. Such for example are the microscopic granules of Altmann and the hypothetical en-

tities conceived by the corpuscular theories of inheritance and de- From this conception of an elementary organism, whether it be a cell, a granule or determinant, has developed very naturally the belief held by many biologists that the solution of all the problems of the organism must be sought in the elementary organism. In other words, the grouping of determinants into systems of higher order (ids, idants of Weismann) or of cells into a multicellular organism _ must be determined solely by the nature of the individual determinants or cells. Because of its nature each elementary organism fits,

so to speak, into a certain place in the whole, as a particular piece _ fits into a certain place in a mosaic. According to this, the preformistic or predeterministic viewpoint, each part or characteristic of the organism is predetermined in the elementary organism or organisms constituting that part. Development is then primarily the realization of these predetermined characteristics quite independently of each other and only after a certain stage is attained do the parts enter into functional relation to each other (Roux, Weismann). So far as the normal individual is concerned, environmental factors are important only in that certain factors are essential to the continuance of life and the progress of the predetermined development. ;

In epigenetic theory the réle of the elementary organism is very different from this. The individual elementary organisms composing a complex organism, e. g., the cells of a blastula, are not necessarily predetermined as different parts, but may be primarily all alike in constitution, the differences which arise being determined by the action of environmental factors upon the whole group and upon each member of it. In the latter case of course relations to other members constitute environmental factors. In short, epigenetic theory conceives the organism as it exists as a product of the reaction between a particular kind of protoplasm, whether in the form of a single cell or of many cells,-and environmental factors. The elementary organism itself represents the product of-such reaction and its grouping with others to form complex organisms involves further reactions of the same sort and their results. From the epigenetic viewpoint then, a particular organism, whether elementary or complex, represents the behavior of a particular protoplasm in a particular environment.

To the vitalist it makes little difference whether the elementary organisms are conceived as primarily alike or different or whether they exist at all. For him the organism is essentially a metaphysical, a ‘supernatural’? phenomenon and its pattern is not primarily a matter of physico-chemical factors of any kind but usually results from the control of physico-chemical factors by the non-mechanistic integrating principle, “entelechy,” “dominant,” “soul” or whatever he may prefer to call it. The question whether organismic pattern is predetermined in the germ or whether it is in each case a reaction of a specific protoplasm to environmental factors is of minor importance to the vitalist, for in the one case the structural pattern, in the other the behavior pattern is metaphysical in origin.

For present purposes it seems unnecessary to distinguish the cell or any other organismic entity as elementary organism. It may merely be pointed out that organisms range in complexity and scale of integration from simple cells or protoplasts, or probably from forms simpler than the ordinary cell, to individuals consisting of thousands or millions of cells, and that even multicellular individuals may be integrated into individualities of still higher order, such as colonies. The cell, it is true, represents a relatively simple form of organism and as such enters into the constitution of more complex forms, but there seems to be no good reason for believing or assuming that it is fundamentally different in origin or pattern from other organisms, whether of a higher or lower degree of integration.

The problem which at present we formulate in terms of heredity versus environment has, in one form or another, occupied the attention of biologists since the time of Aristotle. In earlier times commonly the question whether the organism is wholly preformed or predetermined, it has undergone various changes as regards its terms and the meanings assigned to them. Nearly thirty years ago Whitman (’95) pointed out that it was no longer a question of preformation versus epigenesis, but rather one of the part played by each factor in determining the individual. Even then Weismann, the chief exponent of preformation was forced to admit the effect of environment, as is evident at various points in his writings, and Oscar Hertwig, perhaps his most notable opponent, postulated as necessary for the development of the different species of organisms, “different sorts of primordial substances which possess an extremely complex organization” (Hertwig, ’94, p. 131) and which, because of this organization are capable of reacting specifically and with the greatest exactness to all external and internal stimuli to which they are sub-

id jected. With the development of experimental biology during the last thirty years, the chief difficulty of predeterministic theory has been to account for the variations and modifications in individual development with change in environment, while epigenetic theory has found it difficult to account for the constancy of development and individual pattern, but on the whole there has been still further Predeterministic conceptions of the organism have developed in large part on the basis of zoélogical data and have been perhaps

- more widely accepted by zodlogists than by other biologists. They attained their highest development during what may be called the morphological period in zoélogy in the latter half of the nineteenth century. In fact, they are essentially morphological theories of the organism and attempt to interpret development as a process of construction of a morphological machine by agents or factors inherent in the germ and usually conceived as distinct physico-chemical entities capable of growth and reproduction. According to the Weismannian theory, the most completely developed and most widely accepted of the predeterministic conceptions, each such entity or determinant represents or determines some character of the organism. More recent conceptions call the predetermined entities factors, genes, etc., and hold that, on the one hand, many such factors may be concerned in the development of any particular character, and on the other, that each factor may play a part in the development of more than one character.

In the minds of the earlier preformists there was no doubt that the pattern and course of individual development are predetermined and hereditary. The problem of the individual was not for them a physiological problem, but rather an evolutionary problem and therefore veiled in the mists of the past and belonging to the field of speculation rather than to that of experiment. Most predeterministic theories simply assume the existence of organismic pattern or integration in some terms. Weismann, for example, assumes that the determinants are integrated into groups of higher orders of magnitude, corresponding perhaps to organs, individuals, ete. Roux advanced the hypothesis of qualitative nuclear division as a basis for the orderly and harmonious differentiation of parts and Weismann adopted the idea. Later, however, the experimental investigations of Driesch and many others led Roux himself to abandon the hy-

pothesis. Current theories have advanced far beyond the predeterministi¢ conceptions of Roux and Weismann, but they are still largely concerned with hypothetical hereditary entities of some sort and have little or nothing to say about the integration of these into an organism in development. The accepted view at present maintains on the basis of chromosome behavior in cell division, as well as of experimental embryology, that no sorting out or distribution of genes factors, hereditary potentialities occurs during development. Each cell is regarded as possessing the entire chromosomal mechanism and therefore, as Morgan puts it, “each celi inherits the whole germ plasm” (Morgan, 719, p. 241). In short, current theories of heredity provide no mechanism for individual development and differentiation. Morgan’s discussion of “The Organism as a Whole, or the Collective Action of the Genes” (Morgan, 719, pp. 241-246) does not provide us with any theory of development. The chromosome theory of heredity tells us that each cell inherits the whole germ plasm but as to the manner in which different cells and cell groups become different, it has nothing to say.

Morgan’s discussion of “The Organism as a Whole” is little else than a restatement of the particulate theory of heredity: it does not even define the organism as a whole and the author seems inclined to the view that the wholeness does not exist. The particulate theory of heredity certainly provides no basis for the origin of differences in different cells and cell groups and of physiological correlation between the different parts. But we know that such differences and correlative factors do arise, and if we accept Morgan’s conception of heredity, it is evident that they must originate, either in the reactions of the protoplasm to differences in environment which determine the realization of different hereditary potentialities in different cells or cell groups, or in some ordering metaphysical principle, such as Driesch’s entelechy. In fact, if Morgan is correct in saying that each cell inherits the whole germ plasm, and there is at present no good reason for doubting that this is essentially true, the individual organism, “the organism as a whole” cannot be accounted for in terms of heredity alone, but only in terms of heredity plus behavior, or in terms of metaphysics. Morgan appar ntly fails to distinguish clearly between the hereditary potentialities, the genes or factors of the germ plasm, and the realization of certain of them in the individual organism. No individual represents in its structure and function all the hereditary potentialities of its protoplasm. Each of its parts and each function represents, so to Speak, a particular selection among the hereditary potentialities, and Mor-

gan’s statement provides no basis for such a selection. Morgan’s difficulty appears to be in his belief that the organism as a whole represents in some way “‘the collective action of the genes.” As a matter of fact, such collective action must be the same in all cells since all cells contain the same genes, therefore this collective action alone cannot give rise to local differentiation or to physiological correlation. The individual organism is not the collective action of the genes alone, but originates in some factor which determines what genes shall be concerned in determining the characteristics of each cell or cell group: it is in fact a matter of the action of different genes in different cells, and such differences must be determined, either by environment or by some metaphysical factor. This is equivalent to saying that the individual organism must be a behavior pattern arising in some way in the germ plasm of the species.

In an earlier discussion (Morgan, Sturtevant, etc., 715, pp. 43-44) this distinction between the hereditary potentialities and the realization of different potentialities in different cells seems to be more clearly recognized. There it is stated that we must suppose: “that the Mendelian factors are not sorted out . . . but that differentiation is due to the cumulative effect of regional differences in the egg and embryo reacting with a complex factorial background that is the same in every cell. These regional peculiarities of different parts of the egg and embryo may, like the age of the individual, also be considered as influences external to the hereditary factors which affect the development of characters. And not only

-_- do regional peculiarities influence characters, but special regions are usually required for a given factor difference to manifest itself, just as certain temperatures or ages may be necessary.” If I understand this statement correctly, it is to the effect that development of the individual represents the reaction of the factorial complex to environmental factors. This seems to be Conklin’s viewpoint (’22) and it is essentially the viewpoint of the present book, according to which the physiological gradient constitutes the primary regional differential, to which the factorial complex reacts. This view, however, seems to be very different from that advanced in Morgan’s later book, according to which the organism as a whole represents the collective action of the genes. In this later discussion Morgan appears to leave little or no room for action of the environmental factor, nevertheless the statement quoted above appears without change in the revised edition of his earlier book (1923).

Whether or not one accepts all the details of the chromosome hypothesis, there is of course no necessary conflict between the particulate theory of heredity and the physiological conception of the organism as a whole. They are simply ideas concerning different matters, the one being concerned with the hereditary constitution of the protoplasm of the species, the other with the behavior of this protoplasm in certain environmental relations. It is this behavior

which determines the actual individual. The wholeness of the individual organism lies, not in the relations between genes or factors, but in the relations between different regions, cells or cell groups, in which the potentialities of different genes or groups of genes or factors have been realized. By way of illustration let us consider a very simple, perhaps one of the simplest cases of organization of protoplasm, viz., a mass of protoplasm bounded by a plasma membrane. Some of the microorganisms are very probably little or nothing more than this. Our knowledge of plasma membranes in protozoa and other cells leads

us to believe that any portion of such a protoplasmic mass is capable. of giving rise to a plasma membrane, but as a matter of fact, only in those regions which are in contact with the external medium do the conditions arise which make possible the realization of the potentiality of membrane formation. We say that the plasma membrane results from the exposure of the surface to a medium of a certain physico-chemical constitution and we describe its formation in terms of physical chemistry. But as soon as such a membrane is present, the organism as a whole exists, that is, regional differences which make possible physiological relations between surface and interior exist. All regions of the protoplasm unquestionably possess the hereditary potentiality of membrane formation, but the membrane appears only under certain conditions and in certain regions. In this case the action of environmental factors is obviously necessary to make an organism out of the hereditary potentialities of the protoplasm. Attention may also be called to the fact that the formation of a plasma membrane is non-specific, 7. e., it is not dependent upon the specifie constitution of any particular protoplasm, but all protoplasms give rise under proper conditions to membranes. Un- doubtedly the plasma membranes of different protoplasms differ in their constitution and properties, but the act of formation of a plasma membrane is a non-specific protoplasmic reaction to environmental factors.

In this, the simplest sort of organism, the specific hereditary constitution of each protoplasm concerned is predetermined as regards the individual, though in the course of evolution it too may have been determined in relation to external factors. The actual individual organism, however, as an order and unity of a certain sort and of a certain order of magnitude, is the product of a non-specific, a fundamentally quantitative reaction of that protoplasm to external factors. In short, as regards the individual organism the predeterministic conception fails at the outset.

Turning to a more complex case of a multicellular organism with physiological polarity and symmetry, ¢. g., Planaria, according to current theory as stated by Morgan, all the cells of this animal, as of others, inherit all the genes or factors, including those for head formation, and we know from experiments with pieces that at least certain cells at all levels are capable of giving rise to a head. In the development of the normal animal, however, only certain cells develop as a head while others develop into other parts. Something must determine these differences in behavior of the different cells and parts of the organism, for they occur in spite of the similar nuclear constitution. If we say that these differences between surface and interior in the simplest organisms and in relation to the axes in axiate forms, together with the physiological relations arising from them, are dependent upon physiological polarity and -symmetry, it becomes evident at once that polarity and symmetry of some sort, spherical, radial, or bilateral, constitute the spatial basis of the organism as a whole and the question of their nature and of the physiological processes involved in the determination of the regional differences becomes of fundamental importance in the physiology of development. For the particulate theory of heredity then the question as regards such a form as Planaria becomes the question whether polarity and symmetry are represented by genes or factors.

In the past polarity and symmetry have very generally been supposed to result in some way from molecular or other characteristics of the intimate inherent structure of protoplasm in general. This conception has been stated in terms of crystalline or other stereochemical structure, or sometimes simply in terms of “intimate structure.” If this intimate structure is characteristic of the nucleus as well as of the cytoplasm, polarity and symmetry must represent an even more fundamental feature of protoplasmic constitution than the genes or factors. If on the other hand, polarity and symmetry exist not in the nucleus but in the cytoplasm alone, genes for polarity and symmetry might be assumed to exist. Such genes, however, must behave very differently from others in that they give rise to a general substratum or framework underlying the features determined by

the other genes. Moreover, the difficulty of accounting in such terms for the different polarities and symmetries of different regions and parts of the organism is just as great as for regional differences of other sorts, since the cell inherits the whole germ plasm. In general predeterministic conceptions of polarity and symmetry have usually assumed a molecular or “micellar” structure and orientation, either similar or analogous to that of the crystal or that of the magnet, or of purely hypothetical character, as the basis of polarity and symmetry. Such theories of organismic form have been the subject of much discussion and the analogies between crystals and organisms have been stated repeatedly.’ But even though the crystal does possess a characteristic form and is able to grow, regenerate and undergo “form regulation,” the hypothesis that polarity and symmetry and organismic form are fundamentally similar to that of the crystal meets with various difficulties. Some of these difficulties are briefly pointed out. First, according to stereochemical theory, we should expect organisms to show at least as great a diversity of fundamental axial relations as we find of crystal forms, but as a matter of fact we find only three fundamental morphological patterns among all organisms, viz., radial, polar and polar bilateral, and various modifications and combinations of them (see p. 37). If such patterns were a matter of the molecular constitution, we should expect far greater diversity than this. The varieties of crystalline form in the hemoglobins as described by Reichert and Brown (’09) and the differentiation of the starches (Reichert, 713) show how pattern dependent on molecular constitution varies with that constitution. If polarity and symmetry are patterns of this sort, we ought to expect similar ranges of variation.

Second, the crystal is fundamentally a homogeneous system and the occurrence of chemical change in it is accompanied by the disappearance of crystalline structure. In protoplasm, on the other hand, an extreme degree of heterogeneity exists and growth, maintenance, structure, differentiation and function are all associated with, and dependent upon, chemical reactions. Is not the assumption of an inherent molecular or micellar structure and orientation as the basis of organismic pattern in such as system a priori a highly improbable one? Such pattern is built up by the metabolic reactions;

poco for example Frzibram, 06, 21, for bibliography and for arguments in support of the essential similarity between crystalline and organismic form, The latter paper is concerned to a considerable extent with a hypothetical space lattice. by altering metabolic relations in different regions or cells we can alter it; when the reactions cease only the formal, not the functional Third, from what we know of the constancy of the specific constitution of protoplasm, we should expect a pattern dependent upon specific molecular structure and orientation to be exceedingly stable and but little susceptible to experimental modification. This, however, is far from being the case, as everyone knows. In at least many of the simpler organisms it is possible to obliterate or reverse polarity and to determine new polarities by various experimental conditions (see Chaps. VII-IX), and experimental conditions may also determine whether a particular protoplasm shall give rise to radial or bilateral structures, or both (Chaps. VII, IX). Moreover, polarity and symmetry are less evident in small pieces of the bodies of the simpler animals than in large pieces, and in sufficiently small pieces the original polarity disappears or becomes ineffective, the further development being determined by one or more new polarities dependent upon experimental conditions (Child,’ 07a, ’15¢, pp. 98, 99). And finally, there are cases such as the alga Fucus, in which the polarity of the individual plant is directly determined in the egg or spore by the differential action of incident light (see pp. 58-61).

Fourth, if such a molecular system does exist as the basis of polarity and symmetry and so of organismic pattern, it ought to be possible to obtain some evidence of its existence with the aid of polarized light. Unless the structure of such systems is the same in all directions, and this would be impossible in heteropolar organisms, they must possess optical axes and under proper conditions show some indications of optical anisotropy. During the nineteenth century extensive studies of many animal and plant tissues were made with polarized light,! and it was demonstrated beyond question that many structures of both animals and plants are optically anisotropic. But such structures are predominantly cuticular, non-protoplasmic membranes, shells, skeletal structures, starch grains, crystalloids and fibrillar differentiations, such as muscle, connective tissue, etc. The investigators agree that protoplasm in general, eggs and early developmental stages show no indications of anisotropy. The structure underlying anisotropy evidently arises secondarily in the course of development and, except as regards muscle and