Of all elements, carbon is to us by far the most important and interesting, because this simple substance plays the largest part in all animal and vegetable bodies known to us. It is that element which, by its peculiar tendency to form complicated combinations with the other elements, produces the greatest variety of chemical compounds, and among them the forms and living substance of animal and vegetable bodies. Carbon is especially distinguished by the fact that it can unite with the other elements in infinitely manifold relations of number and weight. By the combination of carbon with three other elements, with oxygen, hydrogen, and nitrogen (to which generally sulphur, and frequently, also, phosphorus is added), there arise those exceedingly important compounds which we have become acquainted with as the first and most indispensable substratum of all vital phenomena, the albuminous combinations, or albuminous bodies (protean matter). We have before this (p. 185) become acquainted with the simplest of all species of organisms in the Monera, whose entire bodies when completely developed consist of nothing but a semi-fluid albuminous lump; they are organisms which are of the utmost importance for the theory of the first origin of life. But most other organisms, also, at a certain period of their existence—at least, in the first period of their life—in the shape of egg-cells or germ-cells, are essentially nothing but simple little lumps of such albuminous formative matter, known as plasma, or protoplasma. They then differ from the Monera only by the fact that in the interior of the albuminous corpuscle the cell-kernel, or nucleus, has separated itself from the surrounding cell-substance (protoplasma). As we have already pointed out, the cells, with their simple attributes, are so many citizens, who by co-operation and differentiation build up the body of even the most perfect organism; this being, as it were, a cell republic (p. 301). The fully developed form and the vital phenomena of such an organism are determined solely by the activities of these small albuminous corpuscles.