538 H. S. Jennings and George T. Hargitt. 



5. Differences in cultural requirements, and other physiological 



differences 



The cultures conducted under uniform conditions for deter- 

 mining the comparative ratesof fission, revealed certain differences 

 in cultural requirements, and in general vitality, among the differ- 

 ent races. In this matter there were likewise diversities between 

 different lines within the same race (a matter to be dealt with 

 elsewhere), but these did not conceal certain characteristic differ- 

 ences in different races. 



Thus in following the descendants of a single individual of 

 the race k for sixty-two days, not a single death occurred in the 

 direct series. For forty-one days of this period there were four 

 parallel series, without a single death in any of them. In the prog- 

 eny of the two typical individuals of this race that were propa- 

 gated thus for sixty-two days, with eight parallel lines, there were 

 but four deaths in the series. In the race 20, on the other hand, 

 which was propagated from two individuals under conditions 

 identical with those for k and parallel with it, for the first thirty- 

 seven days of the experiment, there were twenty-nine deaths in 

 the period of thirty-seven days. In the race Cz in the correspond- 

 ing period of thirty-seven days there were in the progeny of the 

 two individuals eighteen deaths in the direct series.^" 



More striking are the cases of the race D and 4-3- In the case 

 of D, all four series began to sicken and produce abnormalities 

 during the second week of the experiment. They remained in 

 this condition, multiplying slowly, till at about the end of the 

 third week the two lines derived from one of the individuals died 

 out, while the progeny of the other specimen dwindled to a single 

 specimen, which did not divide at all for three days. It finally 

 revived and propagated itself, but in an irregular and abnormal 

 way, producing many abnormalities throughout the rest of the 

 experiment. It was apparent that the uniform cultural conditions 



'" In this period of thirty-seven da>s there were, for each race, four lines of 

 experiments in progress during the first twenty-three days and eight for the last 

 fourteen days. Two additional lines were present for each race, from the fif- 

 teenth to the twenty-eighth days of the experiment. 



