Page:Popular Science Monthly Volume 8.djvu/80

70 every egg is originally a simple cell. The seminal elements of the male are also only simple cells, and the entire mysterious process of fructification is after all nothing but the fusion or concrescence of two different cells, the one a female egg-cell, and the other a male semen-cell. In consequence of this fusion the germs of the two combined cells dissolve, and therewith the young, newly-generated individual begins his existence as a simple cytod, or a small germless ball of protoplasm. But inside of this cytod soon arises a new germ, which turns it again into a cell, and this simple cell forms by oft-repeated segmentation an accumulation of cells. Out of this heap are produced by secretion certain germinal layers or "germ-leaves," and out of these proceed all the other organs of the complete being. Each of these organs again originally consists only of cells, and in all of these cells the essential constituent parts are only the germ and protoplasm: the germ as the elementary organ of propagation and heredity, protoplasm as the elementary organ of all the other functions, sensation, motion, alimentation, and adaptation. Cells and cytods, therefore, are true elementary organisms, independent minute forms of life, which either in the lowest existences continue to live independently, or in the higher organisms combine in numbers to form a community. Cells and cytods are the veritable "formers" of life, or plastids. The most ancient and primordial forms of plastids are cytods, the whole body of which consists of protoplasm, in which the germs are internally produced, and from which therefore the cells proceed.

As a matter of course, to the infinite varieties presented by the organic forms and vital phenomena in the vegetable and animal kingdom, corresponds an equally infinite variety of chemical composition in the protoplasm. The most minute homogeneous constituents of this "life-substance," the protoplasm molecules, or plastidules, as they are called by Elsberg, must in their chemical composition present an infinite number of extremely delicate gradations and variations. The atoms of carbon, hydrogen, nitrogen, oxygen, and sulphur, which compose each of the plastidules, must enter into an infinite number of diverse stratifications and combinations. The chemistry of to-day, with its imperfect methods of investigation, is totally powerless before these intricate organic compounds, and it is possible only to surmise, from the infinitely varied physiological qualities of the numberless kinds of plastids, the infinite variety of plastidules out of which they are composed.

According to the plastid theory recently advanced, the great variety of vital phenomena is the consequence of the infinitely delicate chemical difference in the composition of protoplasm, and it considers protoplasm to be the sole active life-substance. This theory puts force and matter in living organisms into the same causal connection which has long been accepted for force and matter in inorganic bodies. This conception has been rapidly matured, especially in