[CHAPTER VII]
PSYCHIC GRADATIONS
Psychological Unity of Organic Nature—Material Basis of the Soul: Psychoplasm—Scale of Sensation—Scale of Movement—Scale of Reflex Action—Simple and Compound Reflex Action—Reflex Action and Consciousness—Scale of Perception—Unconscious and Conscious Perception—Scale of Memory—Unconscious and Conscious Memory—Association of Perceptions—Instinct—Primary and Secondary Instincts—Scale of Reason—Language—Emotion and Passion—The Will—Freedom of the Will
The great progress which psychology has made, with the assistance of evolution, in the latter half of the century culminates in the recognition of the psychological unity of the organic world. Comparative psychology, in co-operation with the ontogeny and phylogeny of the psyche, has enforced the conviction that organic life in all its stages, from the simplest unicellular protozoon up to man, springs from the same elementary forces of nature, from the physiological functions of sensation and movement. The future task of scientific psychology, therefore, is not, as it once was, the exclusively subjective and introspective analysis of the highly developed mind of a philosopher, but the objective, comparative study of the long gradation by which man has slowly arisen through a vast series of lower animal conditions. This great task of separating the different steps in the psychological ladder, and proving their unbroken phylogenetic connection, has only been seriously attempted during the last ten years, especially in the splendid work of Romanes. We must confine ourselves here to a brief discussion of a few of the general questions which that gradation has suggested.
All the phenomena of the psychic life are, without exception, bound up with certain material changes in the living substance of the body, the protoplasm. We have given to that part of the protoplasm which seems to be the indispensable substratum of psychic life the name of psychoplasm (the “soul-substance,” in the monistic sense); in other words, we do not attribute any peculiar “essence” to it, but we consider the psyche to be merely a collective idea of all the psychic functions of protoplasm. In this sense the “soul” is merely a physiological abstraction like “assimilation” or “generation.” In man and the higher animals, in accordance with the division of labor of the organs and tissues, the psychoplasm is a differentiated part of the nervous system, the neuroplasm of the ganglionic cells and their fibres. In the lower animals, however, which have no special nerves and organs of sense, and in the plants, the psychoplasm has not yet reached an independent differentiation. Finally, in the unicellular protists, the psychoplasm is identified either with the whole of the living protoplasm of the simple cell or with a portion of it. In all cases, in the lowest as well as the highest stages of the psychological hierarchy, a certain chemical composition and a certain physical activity of the psychoplasm are indispensable before the “soul” can function or act. That is equally true of the elementary psychic function of the plasmatic sensation and movement of the protozoa, and of the complex functions of the sense-organs and the brain in the higher animals and man. The activity of the psychoplasm, which we call the “soul,” is always connected with metabolism.
All living organisms, without exception, are sensitive; they are influenced by the condition of their environment, and react thereon by certain modifications in their own structure. Light and heat, gravity and electricity, mechanical processes and chemical action in the environment, act as stimuli on the sensitive psychoplasm, and effect changes in its molecular composition. We may distinguish the following five chief stages of this sensibility:
I. At the lowest stage of organization the whole psychoplasm, as such, is sensitive, and reacts on the stimuli from without; that is the case with the lowest protists, with many plants, and with some of the most rudimentary animals.
II. At the second stage very simple and undiscriminating sense-organs begin to appear on the surface of the organism, in the form of protoplasmic filaments and pigment spots, the forerunners of the nerves of touch and the eyes; these are found in some of the higher protists and in many of the lower animals and plants.
III. At the third stage specific organs of sense, each with a peculiar adaptation, have arisen by differentiation out of these rudimentary processes: there are the chemical instruments of smell and taste, and the physical organs of touch, temperature, hearing, and sight. The “specific energy” of these sense-organs is not an original inherent property of theirs, but has been gained by functional adaptation and progressive heredity.