MULTIPLE INDIVIDUALITY AND NEURON ORGANIZATION

THE principle of multiple individuality underlies the organization of what may be regarded as the basis or counterpart of psychic life,—I mean the nervous system. The multiple systemic structure of neuron organization becomes more emphasized, more clearly defined as we ascend in the scale of evolution. The mode of neuron structure may be regarded as mirroring the mode of organization of psychic life. Although it may appear as a digression in a work on multiple personality to devote space to morphological structure of nerve elements, the reader is asked to bear in mind this important fact of intimate relationship of neuron and mental activity. One mirrors the other. The development of the various forms of neuron structure may be found to correspond or run parallel to the various modes of mental organization. It may, therefore, repay us to give a review of the modes and forms of neuron differentiation and neuron aggregation following the stages of organic evolution.

            In the very lowest forms of animal life there is no nervous system. The neuron has not yet become differentiated, and the primitive cell possesses the fundamental characteristics which are afterward to develop in the highly differentiated functions of the neuron. In the monocellular organism, such as the Amoeba, Paramaecium, Gromia oviformis, Vorticella, and others, there is present a sensitivity to eternal stimulations. Monocellular organisms react to touch, pressure, pricking, temperature, light, and chemical irritations. In the very lowest forms, sensitivity to all kinds of stimuli is diffused and belongs to the protoplasm of the body cell as a whole. The tendency, however, is that the principles of physiological division of labor should work even in the lowest of cells, and without giving rise to any specially formed organs, certain parts of the protoplasm should become more sensitive to certain stimuli than others. In micro-organisms, in infusoria, for example, the pseudopodia or protoplasmic expansions manifest great sensitivity to touch, pricking, temperature, and chemical stimulations; especially is this the case when the protoplasmic expansions become permanent organizations of the animalcule, as, for instance, in the ciliated infusoria in which the cilia show great sensitivity to touch, pressure, and other stimulations.

            The sensitivity shown by monocellular organisms to chemical stimuli may very well correspond to gustatory and olfactory sensations in higher forms, since these senses are of a chemical nature. In fact, we may say that such sensitivity is the germ out of which the senses of smell and taste are developed. Certain pigmented spots of the body of the monocellular organism may become more sensitive to light. Such conditions we find in the Glenodinium polyphemus, Panophrys flavicans, Euglena viridis, and others. These pigmented spots scattered over the body of the monocellular animalcule may be the germs, or, truer to say, the forerunners of the delicate structure of the eye with its highly differentiated function of sight. Of course we must remember the fact that the different organs formed in the higher forms of animal life do not actually come directly as a further development out of the particular spots of the lower micro-organism, but they are probably analogous in function. The structure, of course, is fundamentally different in metazoa from that of the protozoa, but the germs of the different functions are already found in the monocellular organisms. In monocellular organisms the organs are but portions of the cellular protoplasm. Such primitive organs or organoids are to be found in the Amoeba proteus, Paramaecium caudatum, Vorticella, and others.

            In multicellular organisms the organs subserving the highly developed functions are represented by systems of cells, and even by many aggregates of cell-systems, which go to form one funetioning interconnected organic whole, possibly being a sort of syncytium, having cell-bridges and protoplasmic continuity. It is in the multicellular organisms that the nervous system first takes its origin. When organic development reaches a certain height, a group of cells becomes differentiated into a nerve ganglion, spreading out its protoplasmic processes like a network over the organism, and thus supplying with its ramifications every portion of the body. As we ascend the animal series the ganglia become multiplied, groups of neurons increase, and their association and co-ordination increase in number and complexity. In the course of development the neurons, even as the cells of the body in general, become arranged into groups of higher and higher complexity. Groups are aggregated into systems, communities, clusters, and constellations. This holds true of the structure of the higher animals as well as of the general evolutionary series of animal organizations.

            The nervous system appears at first in a disseminated in co-ordinated form, and becomes more co-ordinated as well as more complex with the ascent in the scale of evolution. In the lowest forms this co-ordination of ganglia is merely a matter of repetition, the interrelation of the nerve-centres is at a minimum. What is present is simply a repetition of many ganglia similar, if not identical, both as to structure and function. Co-ordination or concentration is almost absent, so much so that each portion with its ganglion may be completely excised without in the least interfering with the function of the rest. Differentiation of structure and function of the various ganglia is at its minimum, and corresponding with this lack of differentiation is also the lack of co-ordination and integration of the ganglia centres.

            A repetition of ganglia is all that is present in the most elementary forms of neuron organization, and only in the subsequent ascending series of animal life do the separate ganglia become co-ordinated, integrated, and differentiated into a true neuron organization. In this respect neuron organization follows the law of organization in general which proceeds from a repetition of organs with like structure and function to a multiplicity of highly differentiated organs unlike as to structure and function. The lower forms of plants have a repetition of the same organ. The same holds true of animal life, the lower organized forms of the animal series have similarly a repetition of like organs. A similar state we find in the history of the various forms of nervous systems. The lowest form of the nervous system is essentially one of repetition, while the principle of differentiation comes to the foreground in the higher types of animal life. In fact, repetition of organs is taken as a fundamental characteristic of a low stage of development. The structure of the nervous system is systemic or segmental in character. The complexity is at first purely quantitative, and only afterward becomes also qualitative. From complexity of like systems or segments the nervous system progresses to complexity of unlike systems or segments. The diversity of structure and function of the system or segment increases with the course of development.

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