744 PATTERNS AND PROBLEMS OF DEVELOPMENT 



centrations of cyanide interfered with the swelling of the jelly in the frog eggs and 

 decreased permeability in the membrane is the only basis that suggests itself for in- 

 creasing toxicity of cyanide with decreasing concentration. This seems to be the 

 only case known to physiology in which toxicity of KCN increases with decreasing 

 concentration. In the case of the naturally laid and fertiHzed toad egg the membrane 

 and jelly had attained their characteristic condition before the egg was subjected to 

 cyanide. At any rate, it appears highly improbable that opposite relations as regards 

 toxicity and concentration of KCN should exist in two so closely related protoplasms 

 as those of frog and toad. That some factor external to the egg itself is probably re- 

 sponsible for the results with the frog seems certain. 



