RESISTANCE TO HYPOTONIC SEA- WATER 235 



One must be cautious in interpreting this lessened change in elec- 

 trical resistivity in the animal-conditioned media as being the 

 fundamental cause of the longer survival of the worms isolated into 

 such media, because in general we have seen that much greater initial 

 differences in resistivity have relatively little effect upon survival, 

 and also because gelatine suspensions showed a smaller resistivity 

 change than did the controls, and yet had no protective action. 



There is a possibility that if the worms lose contained electrolytes 

 less rapidly into the surrounding medium in the presence of materials 

 from other organisms, organic materials necessary for the continued 

 well-being of the worms, which are not measured by present meth- 

 ods, may also escape less rapidly, as Robertson assumes to happen in 

 the case of allelocatalysis in Protozoa ; and that the observed protec- 

 tion may be due to the retention within the organism of a certain 

 substance or substances necessary for continued existence, rather 

 than to the presence of a definite protective material in the treated 

 solutions. 



We are here dealing with some chemical difference in the medium 

 unanalyzed as yet, rather than with some sort of physical protection 

 of which different types have been described (Allee, 1920, 1926, 

 1927; Drzewina and Bohn, 1928). The material behaves in some 

 aspects like that which Banta and Brown (1929) find affecting the 

 percentage of males in crowded cladoceran cultures, which they 

 attribute to the accumulation of excretory products; in others, like 

 that which Petersen reports as conditioning Paramecium cultures so 

 as to allow higher division rates, especially since the latter has been 

 shown not to be species-specific. We are probably dealing here with 

 the sort of protection which Drzewina and Bohn originally postu- 

 lated in their communication of 1920, quoted at the beginning of 

 this chapter. 



