What is this plasm? What is this mysterious "living substance" that we find everywhere as the material foundation of the "wonders of life"? Plasm, or protoplasm, is, as Huxley rightly said thirty years ago, "the physical basis of organic life"; to speak more precisely, it is a chemical compound of carbon that alone accomplishes the various processes of life. In its simplest form the living cell is merely a soft globule of plasm, containing a firmer nucleus. The inner nuclear matter (called caryoplasm) differs somewhat in chemical composition from the outer cellular matter (or cytoplasm); but both substances are composed of carbon, oxygen, hydrogen, nitrogen, and sulphur; both belong to the remarkable group of the albuminates, the nitrogenous carbonates that are distinguished for the extraordinary size of their molecules and the unstable arrangement of the numerous atoms (more than a thousand) that compose them.
There are, however, still simpler organisms in which the nucleus and the body of the cell have not yet been differentiated. These are the monera, the whole living body of which is merely a homogeneous particle of plasm (the chromacea and bacteria). The well-known bacteria which now play so important a part as the causes of most dangerous infectious diseases, and the agents of putrefaction, fermentation, etc., show very clearly that organic life is only a chemical and physical process, and not the outcome of a mysterious "vital force."
We see this still more clearly in our radiolaria, and at the same time they show us unmistakably that even the psychic activity is such a physico-chemical process. All the different functions of their cell-soul, the sense-perception of stimuli, the movement of their plasm, their nutrition, growth, and reproduction, are determined by the particular chemical composition of each of the 4,000 species; and they have all descended, in virtue of adaptation and heredity, from the common stem-form of the naked, round parent-radiolarian (Actissa).
We may instance, as a peculiarly interesting fact in the psychic life of the unicellular radiolaria, the extraordinary power of memory in them. The relative constancy with which the 4,000 species transmit the orderly and often very complex form of their protective flinty structure from generation to generation can only be explained by admitting in the builders, the invisible plasma-molecules of the pseudopodia, a fine "plastic sense of distance," and a tenacious recollection of the architectural power of their fathers. The fine, formless plasma-threads are always building afresh the same delicate flinty shells with an artistic trellis-work, and with protective radiating needles and supports always at the same points of their surface. The physiologist, Ewald Hering (of Leipsic), had spoken in 1870 of memory as "a general function of organised matter." I myself had tried to explain the molecular features of heredity by the memory of the plasma-molecules, in my essay on "The Perigenesis of the Plastidules" (1875). Recently one of the ablest of my pupils, Professor Richard Semon (of Munich, 1904), made a profound study of "Mneme as the principle of constancy in the changes of organic phenomena," and reduced the mechanical process of reproduction to a purely physiological base.
From the cell-soul and its memory in the radiolaria and other unicellular protists, we pass directly to the similar phenomenon in the ovum, the unicellular starting-point of the individual life, from which the complex multicellular frame of all the histona, or tissue-forming animals and plants, is developed. Even the human organism is at first a simple nucleated globule of plasm, about 1 125 inch in diameter, barely visible to the naked eye as a tiny point. This stem-cell (cytula) is formed at the moment when the ovum is fertilised, or mingled with the small male spermatozoon. The ovum transmits to the child by heredity the personal traits of the mother, the sperm-cell those of the father; and this hereditary transmission extends to the finest characteristics of the soul as well as of the body. The modern research as to heredity, which occupies so much space now in biological literature, but was only started by Darwin in 1859, is directed immediately to the visible material processes of impregnation.
The very interesting and important phenomena of impregnation have only been known to us in detail for thirty years. It has been shown conclusively, after a number of delicate investigations, that the individual development of the embryo from the stem-cell or fertilised ovum is controlled by the same laws in all cases. The stem-cell divides and subdivides rapidly into a number of simple cells. From these a few simple organs, the germinal layers, are formed at first; later on the various organs, of which there is no trace in the early embryo, are built up out of these. The biogenetic law teaches us how, in this development, the original features of the ancestral history are reproduced or recapitulated in the embryonic processes; and these facts in turn can only be explained by the unconscious memory of the plasm, the "mneme of the living substance" in the germ-cells, and especially in their nuclei.
One important result of these modern discoveries was the prominence given to the fact that the personal soul has a beginning of existence, and that we can determine the precise moment in which this takes place; it is when the parent cells, the ovum and spermatozoon, coalesce. Hence what we call the soul of man or the animal has not pre-existed, but begins its career at the moment of impregnation; it is bound up with the chemical constitution of the plasm, which is the material vehicle of heredity in the nucleus of the maternal ovum and the paternal spermatozoon. One cannot see how a being that thus has a beginning of existence can afterwards prove to be "immortal."
Further, a candid examination of the simple cell-soul in the unicellular infusoria, and of the dawn of the individual soul in the unicellular germ of man and the higher animals, proves at once that psychic action does not necessarily postulate a fully formed nervous system, as was previously believed. There is no such system in many of the lower animals, or any of the plants, yet we find psychic activities, especially sensation, irritability, and reflex action everywhere. All living plasm has a psychic life, and in this sense the psyche is a partial function of organic life generally. But the higher psychic functions, particularly the phenomena of consciousness, only appear gradually in the higher animals, in which (in consequence of a division of labour among the organs) the nervous system has assumed these functions.