CONDUCTIVITY AND PERMEABILITY 205 



It was found that recovery from plasmolysis is much 

 slower in CaCl 2 than in NaCl, indicating that the latter 

 penetrates more readily. This is in harmony with the 

 results of measuring electrical conductivity. 



Other experiments indicate that the penetration of 

 NaCl is more rapid in a solution of pure NaCl than it is 

 in a mixture containing NaCl plus Cad 2 , in such propor- 

 tions as to make a balanced solution. This is also in agree- 

 ment with the results of measurements on electrical 

 conductivity. 



Another method of measuring permeability was used 

 by Loeb, 9 who has shown that eggs of Fundulus will float 

 for a time in NaCl 3M , but not, as a rule longer than 3 

 hours. " Before sinking they lose water, as is indicated 

 by the collapse of the membrane and the shrinkage of the 

 yolk sac. Probably some NaCl enters the egg. ' ' In CaCl 2 

 1.25 M, they sink in about half an hour. If, however, 

 they are placed in a mixture of 50 cc. NaCl 3 M + 2 cc. 

 CaCl 2 1.25 M they float for three days or longer. Loeb 

 interprets this as showing that the membrane of the 

 Fundulus egg is practically impermeable to water and to 

 salts in a physiologically balanced solution. But when 

 transferred to a hypertonic non-balanced solution the 

 natural impermeability of the membrane is gradually lost, 

 so that water diffuses out of the egg and its specific 

 gravity is increased to such an extent that it sinks. This 

 action, and likewise the entrance of NaCl into the egg, 

 is prevented by the addition of small amounts of CaCl 2 . 



A very interesting series of experiments was made by 

 S. C. Brooks, using the following methods: (1) diffusion 

 through living tissue, (2) exosmosis, (3) change of curva- 

 ture of strips of tissue. 



8 Loeb (1912, C, D). 



