LIVING SUBSTANCE 



When the contents of protoplasm are investigated, upon super- 

 ficial examination two groups of constituents may be 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, e.g., 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 Gregarince (Fig. 



22, V). 



a. The Solid Constituents of Protoplasm 



The solid constituents of protoplasm 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 role 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 

 ground-substance of the protoplasm (Fig. 



23, a), give to the plant-cell and thus to 

 the whole plant its magnificent green 

 colour, for their delicate albuminoid bodies 



are saturated with an intensely green colouring-matter. The chloro- 

 phyll-bodies are of the greatest importance for the plant-cell, for in 

 them occurs a considerable part of its characteristic vital process. 

 Other organoids, which in many cases are likewise of great import- 

 ance for the cell-life, are the drops of liquid, or vacuoles, as they are 



G 



Fia. 23. a, A plant-cell contain- 

 ing chlorophyll-bodies. 6, A 

 chlorophyll-body undergoing 

 division. (After Sachs.) 



