PROTOZOAN differences: resistance to heat 



137 



Paramecium caudatum Blepharisma lateritia 



Paramecium aurelia Spirostomum teres 



Paramecium bursaria Urostyla grandis ?) 



Fig. 1 



the species. However, the resistance of P. aureha appears to be 

 distinctly higher than that of P. caudatum. The modes of the 

 two curves are two degrees apart. This difference in their resist- 

 ance to heat, together with the fact that they react differently 

 to carbon dioxide (Jacobs '12), may perhaps be considered further 

 evidence of the distinctness of the two species. In the case of 

 P. caudatum and P. bursaria it will be seen that the modes of 

 the two curves coincide, but the shape of the curve is quite 

 different. Although the greatest number of deaths occur at the 

 same point, yet there is a characteristic difference in that P. 

 caudatum shows more individual variation within the species. 

 This may be due, however, to the fact that a much larger num- 

 ber of individuals from a greater variety of sources were em- 

 ployed than was the case with P. bursaria. The curve for Ble- 

 pharisma is peculiar in that there is no one point which stands 

 far above the others, but there are three points comparatively 

 close together giving the curve a flattened appearance. This is 

 accounted for by the fact that in the cultures in which it devel- 



