BEGINNINGS OF CO-OPERATION 79 



and what kind of fodder he was feeding his washed 

 protozoans. 



The resuhs of varying the amount of food are 



REPRODUCTION-RATE FOR 24 HOURS WHEN ONE OR TWO OXYTRICMA 

 ARE SEEDED INTO TWO DROPS OF P. FLUORESCENS 



CONCCMTRN 4 X 



seeoiNG t 2 



8.0 tO.2 tO.6 10.4 



Fig. 12. In the denser suspensions of bacteria the 

 protozoans divide more rapidly when cultures are inocu- 

 lated with two protozoans than if started with a single 

 individual. (From Johnson.) 



shown in Figure ii. With X concentration, in 

 twenty-four hours one animal produced about eleven 

 progeny. With 2X concentration, isolated sister cells 

 produced nine, and with a 4X concentration other 

 isolated sister cells produced but three and a half. 

 The rate of reproduction also decreased when less 

 than X bacteria were present. 



