EFFECT OF EXCRETION PRODUCTS OF PARAMAECIUM 565 



mals on the various amounts of medium were about thirty genera- 

 tions apart, so that it might be suggested that this offered an ob- 

 jection. 



The volumes of medium selected were two, five, twenty, and 

 forty drops. The same pipet was used in measuring the liquid in 

 all the work, and so practical uniformity was attained. Infusions 

 of hay were used as a culture medium and the organisms were 

 isolated on slides of different capacities, depending on the amount 

 of liquid employed. The slides were kept in moist chambers to 

 prevent evaporation. 



The daily rate of division of the organisms in two, five, twenty, 

 and forty drops of culture medium changed every twenty-four hours 

 showed that, for example, those in five drops divided 2.4 per cent 

 more rapidly than those in two drops, those in twenty drops 

 divided 6.4 per cent more rapidly than those in two drops, and 

 those in forty drops divided 7.4 per cent more rapidly than those 

 in two drops (fig. 4, part A). The details of each of the four ex- 

 periments (A, B, C, D) are evident in fig. 2 which shows the rate 

 of division of each of the lines on the different amounts of medium 

 averaged for each four days of the experiment. Experiments 

 B and C are the most important ones because these comprised 

 cultures on all the volumes of medium. A was carried to test the 

 general method to be used, and D was carried to check up certain 

 data. 



It is believed that the experiments are sufficiently comprehen- 

 sive clearly to establisfi the fact that the rate of reproduction of 

 specimens from pure lines of paramaecia, when bred under identi- 

 cal conditions of temperature and culture medium, is influenced 

 by the volume of the culture 7nedium {within the limits tested in the 

 experi7nents) , and that the greater the volume the more rapid is the 

 rate of division. 



It being clear that in an increased volume of culture medium 

 there is an increased division rate, the next point of importance is 

 to determine to what factor or factors this is due. It is evident 

 that it may be brought about by variations in 1, temperature; 2, 

 pressure; 3, surface of medium exposed to atmosphere; 4, food 

 supply; 5, excretion products of bacteria; or 6, excretion products 

 of paramaecia. 



