STRUCTURAL BASIS OF PROTOPLASM 17 



"nucleus" and "cell-body" are therefore only topographical expres- 

 sions, and in a measure the same is true of the terms "karyoplasm " and 

 " cytoplasm." The latter, however, acquire a special significance from 

 the fact that there is on the whole a definite chemical contrast be- 

 tween the 'nuclear substance and that of the cell-body, the former 

 being characterized by the abundance of a substance rich in phos- 

 phorus known as miclein, while the latter contains no true nuclein and 

 is especially rich in proteids and related substances (nucleo-albumins, 

 albumins, globulins, and others), which contain a much lower per- 

 centage of phosphorus. 



The differentiation of the protoplasmic substance into nucleus and 

 cytoplasm is a fundamental character of the cell, both in a morpho- 

 logical and in a physiological sense ; and, as will appear hereafter, 

 there is reason to believe that it is in a measure the expression of 

 a corresponding localization of the operations of constructive and 

 destructive metabolism which lie at the basis of the individual cell- 

 life. A third element, the centrosome (Figs. 5-7), present in many 

 if not in all cells, is especially concerned with the process of division 

 and cell-reproduction. Recent research has rendered it probable that 

 in point of morphological persistency the centrosome is comparable 

 with the nucleus ; but this conclusion is not yet definitely established. 



B. STRUCTURAL BASIS OF PROTOPLASM 



As ordinarily seen under moderate powers of the microscope proto- 

 plasm shows no definite structural organization. A more precise ex- 

 amination under high powers, especially after treatment with suitable 

 fixing and staining reagents, reveals the fact that both nucleus and 

 cytoplasm possess a complicated structure. Regarding the pre- 

 cise nature of this structure opinion still differs. According to the 

 view most widely held/ one of its essential features is the presence 

 of two constituents, one of which, the ground-substance, cyto- 

 lymph, or enchylema, is more liquid, while the other, the spongio- 

 plasm or rcticitlum, is of firmer consistency, and forms a sponge-like 

 network or alveolar structure extending everywhere through the more 

 liquid portion. At the present time it seems probable that the 

 more solid portion is the more active and is perhaps to be identified 

 as the living substance proper, the ground-substance being passive ; 

 but the reverse of this view is maintained by Leydig, Schafer, and 

 some others. The most elaborate and painstaking investigation has 

 moreover failed to determine with absolute certainty even the physi- 

 cal configuration of the network. 



Biitschli and a considerable school of followers among both 



