578 LORANDE LOSS WOODRUFF 



tion, the infusion from the flask minus the paramaecia was simi- 

 larly filtered so that there could be no possibility of error through 

 the filtration process affecting the bacterial content or contami- 

 nating the infusion. Further, since in the culture medium F+P 

 the paramaecia had undoubtedly decreased the number of bac- 

 teria present through feeding on them, the fluid, after the ani- 

 mals were strained out, was inoculated with bacteria from the 

 medium F —P, and as an added precaution F — P was inoculated 

 with bacteria from F +P. Thus, while the bacteria were reduced 

 in F-\-P through being eaten by the animals, this medium un- 

 doubtedly contained more food for bacteria, and therefore, when 

 inoculated, should develop bacteria more rapidly than the /^ — P 

 culture medium, and therefore there would be at least as much 

 food for the organisms on which the experiments were made in 

 F+P as in F-P. 



It is believed then that, when the media were employed in the 

 experiments, they were practically identical except that one con- 

 tained the products of metabolism of a heavy growth of paramae- 

 cia while the other was absolutely free from such contamination. 



The results of this experiment are shown graphically in fig. 10. 

 A shows the results of a preliminary observation which includes 

 the daily isolations for four days. B illustrates the results from 

 another and longer experiment made by the reisolation of both 

 series from the main pedigree cultures A. C gives clearly the 

 same general results which were obtained when the whole experi- 

 ment was repeated, this time with new flasks of culture medium, 

 etc. 



As a further check on the results, fig. 10, B shows that, when 

 after eight days subjection to the F+P medium, another culture 

 was isolated line by line from it and put on the F—P medium, 

 the division rate approached the rate of that continuously on 

 the F—P medium. And again when still another culture was iso- 

 lated from the culture recently transferred from theF — Pmedium, 

 and put back on the F +P medium, the rate of division of this new 

 culture approached that of the series which had been continually 

 on the P+P medium. 



A short series of experiments for comparison was made with 



