SELECTIVE PERMEABILITY 83 



agents. The same result might be 

 brought about by physical means, espe- 

 cially where structural changes occur 

 which alter the permeability of the 

 plasma membrane at the surface of the 

 protoplasm or of internal structures 

 (such as the nucleus and plastids) in 

 such a way as to bring together sub- 

 stances which do not normally react. 



By means of electrical measurements 

 we can follow changes in the cell with 

 suflScient accuracy to enable us to give 

 a mathematical expression to certain 

 fundamental ideas of biology which have 

 never been precisely formulated. Among 

 these are such important conceptions as 

 vitality, injury, recovery, and death. A 

 mathematical theory of the mechanism 

 of injury and recovery has likewise been 

 developed by the writer. 



We find that some aquatic organisms 

 are killed when placed in a solution of 

 common salt, but that death can be 

 hindered by the addition of a lime salt. 

 We speak of this as antagonism between 



