580 



LORANDE LOSS WOODRUFF 



the same two culture media on the pedigree culture of P. caud- 

 atum, and this gave the same general result. In this experiment 

 the animals on the F +P medium died out (fig. 11). 



It is obvious then from these data that culture media in which 



Fig. 11. Record of an experiment to determine the effect of a medium, which 

 has supported a rich growth of Paramaecium aurelia, on the rate of reproduction 

 of P. caudatum. The ordinates represent the average daily rate of division of the 

 four lines of organisms, again averaged for four day periods. Rate of division 

 of organisms in culture medium free from the excretion products of P. aurelia 

 ( — P) = , culture medium with excretion products (+P) = •••• 



paramaecia have been living has a decidedly depressing effect on the 

 rate of reproduction of paramaecia of the same pure pedigree stock 

 as the contaminating animals, as well as on the rate of reproduc- 

 tion of another species, P. caudatum. 



