STUDIES IN ARTIFICIAL PARTHENOGENESIS. 



359 



3. Sttgar and Glycerin. A solution of cane sugar possesses a 

 surface tension very slightly above that of pure water, 1 a glycerin 

 solution has a surface tension below that of sea-water. Thus, 

 both of these solutions have a lower surface tension than sea- 

 water, but if eggs are placed in them, no membrane elevation 

 occurs. The reason for this exception will be considered shortly. 



I have shown that membrane elevation depends upon a lower- 

 ing of surface tension, and I shall now consider the mechanism 

 of the process. As has already been pointed out, the unfertilized 

 egg is surrounded by a membrane, which is probably a gel or 

 semi-gel. In the appended diagram, ABCD represents this gel, 



whose parts pull on each other by reason of their surface tension. 

 As a result of this pull, the underlying egg contents, and more 

 especially the peripheral portions of the egg, are under pressure. 

 This pressure inward is compensated by a "Quellung-druck" 

 due to a tendency of the proteins to swell. Upon a diminution 

 of surface tension, the pressure inward is relaxed and the protein 

 or proteins directly beneath the membrane immediately swell, 

 thus pushing out the membrane. If the surface tension remains 

 lowered, the entire egg swells, and cytolysis results. 



It w y as found that not all low r erings of surface tension produced 

 membrane elevation, there being three types of exceptions. The 

 reason for these exceptions can now be explained. Although 

 many colloids lower surface tension, they are unable to diffuse 



1 Forch, loc. cit. 



