THE CELL 279 



in the gel condition, the one in which we usually find it in cells 

 according to BOROWIKOW. 



With the occurrence of death protoplasm gelatinizes, Brownian move- 

 ment of the smaller particles ceases, and the structure of the gel 

 appears in the ultramicroscope as a conglomeration of many re- 

 flecting platelets. It makes a substantial difference whether the 

 protoplasm slowly dies or is suddenly killed by a fixative (alcohol, 

 formalin, etc.). In the first instance there is a precipitation (floccu- 

 lation), whereas, in the latter there is a stiffening; this difference 

 may be readily recognized under the ultramicroscope. 



From this we may understand why a dead plant cell simply bursts 

 in water, for the defects are no longer repaired from within. The 

 cell contents have been already gelatinized. Chloroblasts (chlorophyl 

 granules) may be assumed to possess colloidal properties similar to 

 protoplasm; only it seems the latter are more delicate (PONOMAREW). 

 The living protoplasm of many animal cells, however, seems to exist 

 as a gel. At least in monocellular organisms, blood cells, etc., A. 

 MAYER and G. SCHAEFFER* could not discover any Brownian move- 

 ment of certain granules. 



On account of the great differentiation of animal cells, more com- 

 prehensive investigations must be awaited; thus it appears to me 

 probable that red blood cells have viscous contents (see p. 305). 



The Nucleus. 



We know even less about the colloidal nature of the nucleus than 

 of protoplasm. Ultramicroscopically, the nucleus appears to be a 

 complex of hydrosols containing larger particles and to be quite 

 poor in water. This corresponds well with the picture produced by 

 staining. 



The colloids of cell protoplasm seem to be rather indifferent 

 chemically; they are poorly stained by both acid and basic dyes. 

 The nucleus, or more properly the chromatin substance, seems to 

 possess pronounced acid properties, which are manifested by its 

 intense staining with basic dyes (see A. KOSSEL*). 



The Cell Membrane and the Plasma Pellicle. 



The cell pellicle imparts its shape to the fluid protoplasm which 

 otherwise would be spherical as the result of surface tension. The 

 cell pellicle occurs in plants especially. In animals an interior 

 skeleton or a spongy framework may determine shape. Theory 

 requires an additional invisible plasma pellicle as bounding the 



