. General physiology; an outline of the science of life. LIVING SUBSTANCE 81 When the contents of protoplasm are investigated, upon super- ficial examination two groups of constituents maybe distinguished, namely, various well-defined bodies, such as grains, droplets, etc., and a uniform, semi-liquid, apparently homogeneous ground- substance, in which the former, like the nucleus, lie embedded. But, while in many cells the ground-substance contains only a few solid bodies, as, , in many epithelium-cells (Fig. 22, a), in others it can scarcely be seen because of the abundant granular consti
. General physiology; an outline of the science of life. LIVING SUBSTANCE 81 When the contents of protoplasm are investigated, upon super- ficial examination two groups of constituents maybe distinguished, namely, various well-defined bodies, such as grains, droplets, etc., and a uniform, semi-liquid, apparently homogeneous ground- substance, in which the former, like the nucleus, lie embedded. But, while in many cells the ground-substance contains only a few solid bodies, as, , in many epithelium-cells (Fig. 22, a), in others it can scarcely be seen because of the abundant granular consti- tuents, as is frequently the case in many plant-cells, and especially in certain parasitic unicellular organisms, the Gregarina: (Fig. a. The Solid Constituents of Protoplasm The solid constituents of inotoijlasm are material elements of very various natures; they are special constituents, and do not occur in all cells. Among them occur bodies that are of the highest significance for the life of the cell in which they are contained, that impress upon the cell a characteristic feature; and also elements that play no role whatever in the vital process, such as the indigestible residue of food. There are found, further, food- constituents which are not yet changed, other substances which have been regularly transformed from the food by the vital process or have been formed anew, and, finally, in many cells independent organisms which live continually in them as symbionts or parasites and under cer- tain circumstances play a definite rdle in the life-process of the cells. Among the solid protoplasmic constitu- ents which are especially significant in the life of the cell, and which, therefore, can be considered as organs of the cell, or, better, since we understand by organ a structure composed of many cells, as cell- organoids, the chlorophyll-bodies of plant- cells are especially important. These small, usually roundish, sometimes band- shaped bodies, which lie embedded in the
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