PROTOZOAN differences: resistance to heat 



14] 



.^_— — — — Paramecium caudatum Pure line no. t 



Paramecium caudatum Pure line no. 6 



Paramecium caudatum Pure line no. 5 



Fig. 2 



February 17 (just three weeks after the culture was started) 

 gave these results: 



At 36° there were 8 deaths in a total of 76 

 At 37° there were 35 deaths in a total of 120 

 At 38° there were 130 deaths in a total of 130 



In another experiment on March 30 (during the period of 

 depression) : 



At 30° there were 5 deaths in a total of 40 

 At 37° there were 11 deaths in a total of 28 

 At 38° there were 19 deaths in a total of 19 



One may see the effect of the depressing influence by comparing 

 the totals present in the same quantity of the medium on these 

 dates. Evidently, whatever factor influenced this race in such 

 a way as to interfere with its development, had no effect on its 

 resistance to heat. In spite of unfavorable medium, the curve 

 for Race 5 represents the normal condition of a distinct race or 

 * biotype, and one is led to infer that different biotypes of P. 

 caudatum may have different powers of resistance to heat. At 



