NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 285 



nuclear size as follows. Under normal conditions the quotient 

 obtained by dividing nuclear volume by cytosomal volume (the 

 Kernplasmarelation, K/P) has a certain value (the Kernplas- 

 manorm). Any disturbance of this ratio, due to a change in 

 either nuclear or cytosomal volume, leads to a condition of ten- 

 sion (Kemplasmaspannung). This tension is a factor in the cell 

 physiology, and leads to certain consequences, some of which 

 Hertwig pointed out. 



APPLICATIONS OF THE IDEA 



Other investigators have applied the conception to a variety of 

 fields. A fair notion of the importance attached to changes of 

 the Kernplasmarelation can only be gained by contemplating the 

 wide range of phenomena which biologists have sought to ex- 

 plain on this basis or which have a bearing on the ratio. The 

 list which follows is incomplete. 



1. Size of cell. The work of Gerassimow and of Boveri has 

 already been cited. Godlewski ('08) attributes giant cells in 

 echinoderms to an increase of nuclear material. Hegner ('19, 

 '20) finds nuclear volume in Arcella related both as cause and as 

 effect, to cell size, and Popoff ('09 a) explains changes of size in 

 Paramecium by changes in the value of K/P. 



2. Physiology of cell. Hertwig ('03) conceived the idea that 

 increase of cell activity is associated with (causes?) an increase of 

 relative nuclear volume. A decrease of nuclear ratio has been 

 held responsible for senescence (Minot, '08). The nucleus en- 

 larges in the degeneration of Amoeba (Prandtl, '07). 



3. Cell division. Changes of the ratio K/P may cause or 

 postpone cell division, according to Hertwig ('08), and it makes 

 no difference whether the change in the ratio is due to changes in 

 nuclear volume or to changes in cytosomal volume. Geras- 

 simow's similar conclusion has already been mentioned. Popoff 

 ('08, '09) discovered a regular decrease^ of relative nuclear volume 



2 Some confusion has been introduced into the literature by the fact that 

 Popoff, Godlewski, Rautmann, Eycleshymer, and Metcalf express the nucleo- 

 plasma ratio as the quotient of the cytosomal volume divided by the nuclear 

 volume (P/K), whereas all other authors follow Hertwig in placing the nuclear 



