Disease and Immunity 87 



he could raise the temperature still higher. At 

 78 degrees he found another sticking point which 

 he could not get by for eight months without 

 causing deaths. But past this point progress 

 was much more rapid. Several other sticking 

 points were found, but he finally got these ani- 

 mals to live in water at 158 degrees, when the 

 experiment was terminated by accident. 



Here is an example of these little animals de- 

 veloping their powers of resisting the action of 

 heat on their protoplasmic substance by exercis- 

 ing such powers as they had in the beginning, 

 and such as they acquired on the road. In that 

 process they gained powers continually under in- 

 creasing load, but they died when the load was 

 raised to an overload. 



Czerny found that by a very gradual addition 

 of salt he could get amoebae to live in a four per 

 cent solution, but that none could survive when 

 placed directly in a two per cent solution. The 

 two per cent solution was an overload for amoeba 

 which had lived in pure water, but four per cent 

 of salt was less than an overload after the 

 amoebae had developed their powers by exercising 

 them. 



