The Material Substratum of Life
The Synthetic Concept of the Individual in Biology
According to the materialistic theories of life, of which Haeckel is the most noted supporter, life was derived from a form of matter, protoplasm, which not only has a special chemical composition, but possesses further the property of a constant molecular movement of scission and redintegration; vital metabolism or interchange of matter, by which the molecules are constantly renewed at the expense of the environment.
It was Huxley who defined protoplasm as the physical basis of life; and, as a matter of fact, life does not exist without protoplasm.
But Schultze and Haeckel carried this doctrine further, to the point of maintaining that a minute particle of protoplasm was all that was needed to constitute life; and that such a particle could be formed naturally, whenever the surrounding conditions were favorable, like any other inorganic chemical substance; and in this way the materialists endeavoured, with great ingenuousness, to maintain the spontaneous origin of life. And when Haeckel thought that he had discovered the moneræ or living cells composed of a single particle of protoplasm, he held that these were the first species to have appeared on earth.
But the further researches of physiologists and the improvements in the technique of the microscope proved that protoplasm does not exist independently in nature; because living cells are always a combination of protoplasm and a nucleus. If the nucleus is extracted from a radiolarium, the latter mortifies, and the protoplasm also dies; if an amœba is severed in such a manner that one part contains nucleus and protoplasm and the other protoplasm alone, it will be found that the latter part mortifies and dies, while the first part continues to live. If an infusorium is divided in such a way that each of the separate sections contains a part of the nucleus and a part of the protoplasm, two living infusoria are developed similar to the original one. Experiments of this kind, to which Verworn has given high authority, serve to prove that life does not exist except in cells divisible into protoplasm and nucleus. Further discoveries confirm this theory, as for instance the presence of a nucleus in hemocytes or red blood corpuscles, which were formerly believed to be instances of anuclear cells; and the discovery of protoplasm in microbes, which had formerly been considered free nuclei.
Now, when we have an independent living cell, it represents an individual, which not only has, as a general feature, this primitive complexity of parts, but also certain special characteristics of form, of reaction to environment, etc., that mark the species to which this particular living creature belongs.
Accordingly, we cannot assert, without committing the error of confining ourselves to a generic detail, that life originates in protoplasm or in a combination divisible into protoplasm and nucleus; we should say that life originates in living individuals; since, aside from abstract speculation, there can be no other material substratum of life.
Such a doctrine is eminently synthetic, and opens the mind to new conceptions regarding the properties that characterise life.
Formerly when life was defined as a form of matter (protoplasm) subject to constant movement (metabolism), only a single general property had been stated; for that matter, even the stars consist of matter and movement; and, according to the modern theory of electrons, atoms are composed of little particles strongly charged with electricity and endowed with perennial motion. Accordingly, these are universal characteristics, and not peculiar to life; and metabolism may be regarded as a variation of such a property, which is provoked by, or at least associated with the phenomenon of life.
The properties which are really characteristic of life have been summed up by Laloy in two essential groups; final causes and limitations of mass, or, to use a term more appropriate to living organisms, limitations of form and size.