446 H. S. JENNINGS AND K. S. LASHLEY 



in Experiment 16 but 73 out of 482 members of pairs, orlS.lper 

 cent, are dead at the end of twenty-seven days (see table 44). 



The question will naturally be asked whether this difference 

 has anything to do with the completion of conjugation in the one 

 case, and its lack in the other; whether comparison of the two 

 experiments indicates that the ex-con jugants are more vigorous. 

 To this question the answer no must be given; no conclusion what- 

 exev can be drawn on this point from comparing the two experi- 

 ments. The grounds for this are as follows : 



1. The matter was directly tested by a later experiment in 

 which both pairs and split pairs came from the same source as 

 the split pairs of Experiment 17, the two sets being subjected 

 throughout to identical treatment. This later experiment, 

 beginning June 11, 1912, was planned for the purpose of comparing 

 the fission rate and mortality of members of pairs and of split 

 pairs for a long period, under identical conditions; as it turned out, 

 it gave data only on the relative mortality of the two. The experi- 

 ment included 130 pairs (260 lines), and 122 split pairs (244 hues), 

 making in all 504 lines of propagation. 



The mortality was much higher than in experiment 17, and 

 affected pairs and split pairs to nearly the same extent, though 

 with a slight advantage in favor of the split pairs. On June 

 17 there remained alive but 34 out of 260 lines descended from 

 pairs, or 13.1 per cent; of the split pairs 48 out of 244, or 19.7 

 per cent still survived. The experiment was then abandoned, 

 since the survivors were too few to give valuable data on the 

 fission rate. 



The difference between Experiments 16, 17, and this later 

 one in respect to mortality was clearly due to differences in the 

 conditions. In Experiment 16 the animals came from relatively 

 pure water, and the experiment was carried on in cool weather; 

 the mortality was low. In experiment 17 and the later one the 

 animals came from extremely foul water (mouth of a sewer), 

 and the experiments were carried on in hot weather; the tempera- 

 ture being still higher in the later experiment (June 11 to 17) 

 than in Experiment 17 (May 9 to 30). The mortality became 

 greater as summer came on; a result in accordance with much 



