LIVING SUBSTANCE 



25 



chromatin, of which they are composed, appears in the form of gran- 

 ules. Some of these are especially conspicuous and are then called 

 pseudonucleoli. Other masses of chromatin, the true nucleoli, are 

 sometimes found embedded in the nuclear sap. If the cell is stained 

 with such dyes as hematoxylin or safranin, the nucleus is made to 

 stand out prominently against the light protoplasmic ground-sub- 

 stance. The nucleus, however, does not absorb the pigment very 

 evenly, because the chromoplasmic network and nucleoli possess a 

 much greater affinity for it than the matrix. Herein really lies the 

 reason for saying that the cell is composed of chromatic and achromatic 

 substances; the former combine with many dyes with great ease 

 while the latter do not. 



Attraction-sphere enclosing two centrosomes 



Plastids lying in the 

 cytoplasm 



Nacleus 



Vacuole 



Passive bodies (meta- 

 plasm or paraplasm) 

 suspended in the cy- 

 toplasmic meshwork 



Fig. 2. — Diagram of a Cell. (Wilson.) 



The Chemistry of the Cell. — The chemical analysis of protoplasm 

 as practised at the present time, necessitates its destruction as a 

 functional entity. For this reason, its composition can only be 

 deduced from that of dead organic material. KosseP divides its con- 

 stituents into primary and secondary, the latter being present only 

 in some types of cells. As an example of this kind might be mentioned 

 the glycogen of the cells of the liver. As primary constituents are 

 to be regarded lecithin, cholesterin (lipoids), proteids (nucleopro- 

 teids), inorganic salts and water. 



As lipoids must be classified all those bodies which may be extracted with ether 

 or similar solvents.^ Whether the lecithin which belongs to the class of the 

 phosphatides, is actually a primary constituent of the cells is still doubtful. It is 



1 Archiv fiir Anat. und Physiol., 1891. 



^ Overton, Studien iiber die Narkose, Jena, 1901. 



