136 



ROBERT H. HUTCHISON 



TABLE 5 

 Spirostomum teres 



struct a curve for Spirostomum teres in the following way: 

 Between 40° and 41°C. 8 per cent of the deaths occurred. This 

 point is marked on an ordinate halfway between 40° and 41°. 

 Between 41° and 42° C. 43 — 8 per cent or 35 per cent of the 

 deaths occurred and this is marked on an ordinate halfway 

 between 41° and 42°. At a temperature between 42° and 43°C. 

 100 — 43 per cent or 57 per cent of the deaths occurred. This 

 number 57 is represented on an ordinate halfway between 42° 

 and 43°. Lines drawn connecting these points give the curve for 

 Spirostomum shown in figure 1. The curves for the other forms 

 are constructed in the same manner. 



Of these six species Paramecium caudatum is seen to be the 

 most variable. The animals experimented with were taken from 

 several different cultures, all of which had been seeded with mate- 

 rial from a pond. The curve for Paramecium aurelia is based 

 upon figures obtained partly from one pure line culture and partly 

 from one or two mixed cultures. It is probable that experiments 

 with more cultures of this species would give a little more spread 

 to the curve, that is, would show a little more variation within 



