214 



ROBERT H. HUTCHISON 



TABLE 2 



The effect of M/50 NaCl on the heat resistance of P. caudatum from an alkaline 



medium 



It will be noted from the tables that M/lOO NaCl has raised 

 the mean of the fatal temperature zone of this pure line 1.13°C., 

 and that M/50 NaCl has raised it 1.8°C., the stronger concen- 

 tration producing a slightly greater effect. Concentrations 

 stronger than M/50 had a toxic effect on this race, deaths occur- 

 ring at much lower temperatures than the controls. The effect 

 of KCI was not studied except that it was found in one experi- 

 ment that M/200 KCI had a toxic effect, all the animals being 

 dead at 38°C. In weaker concentrations it would probably 

 have shown some pro'tective action. 



Solutions of CaCl2 were tested on this same race, and weak 

 concentrations had a marked protective action. When trans- 

 ferred to M/300 CaCli nearly all the Paramecia died within 

 two hours at room temperature, while in M/3000 CaCla this 

 race remained alive at room temperature for at least two weeks. 

 Table 3 shows the effect of CaCl2 alone, and table 4, the effect of a 



