EFFECT OF FOOD ON GROWTH OF PARAMECIUM CAUDATUM. 85 



laboratory for several months; race B came from a culture pro- 

 cured from the University of Pennsylvania; race C came from 

 Powers and Powers, Nebraska; race D, was a wild race recently 

 obtained from a pond in the neighborhood of the college labora- 

 tory. 



A comparative study of pure lines from these four races was 

 carried on with the addition of yeast both whole and ground to 

 the food substance. Two drops each were used. Malted milk 

 remained the basic food substance. 



TABLE V. 



A. LABORATORY CULTURE IN SPRING WATER. Daily Division Average For Six 



Day Periods. 



These individuals had previously undergone a period of star- 

 vation living in the laboratory under adverse conditions. Here 

 the malted milk alone seemed more favorable to growth without 

 the addition of whole yeast. It will be observed, however, that 

 when ground yeast was added that there was a distinctly marked 

 increase in the division rate. 



TABLE VI. 



B. LABORATORY CULTURE IN HAY INFUSION. Daily Division Average For Six 



Day Periods. 



The same result may be seen as in Table V., where the Para- 

 mecia had been in hay infusion. 



