386 



Annals New York Academy of Sciences 



in the absence of folic acid, may be subcultured indefinitely. Particle free 

 animals, on the other hand, show an absolute requirement for this substance, 

 as judged from their inability to grow beyond the second transfer. 



Particles may produce sufficient quantities of folic acid to provide for the 

 nutritional needs of the protozoan. To test this possibihty, particle bearing 

 animals were treated with penicillin in the presence and the absence of folic 

 acid (table 6). As expected, particle free animals did not grow in the con- 



Table 5 

 Vitamin Requirements of Paramecium 



Table 6 



The Effect of Penicillin upon the Folic Acid 

 Requirement of Paramecium 



/ 



* Animals particle free. 



trols, or in penicillin-treated tubes in the absence of folic acid. Addition of 

 folic acid to the medium restored the ability of these animals to grow in the 

 presence or absence of peniciUin. Particle containing animals, on the other 

 hand, failed to grow in folic acid free medium containing penicillin, whereas 

 animals under similar conditions retained their particles and grew well in the 

 absence of penicillin. (Irowth of particle bearing animals in which folic acid 

 was present in both the control and penicillin-treated tubes was good. Peni- 

 cillin-treated animals contained no particles. Subsequent deletion of folic 

 acid from the medium containing these penicillin-treated animals resulted in 

 \ the death of the protozoan. These data support the view that folic acid pro- 



