Soldo: Axenic Culture of Paramecium 



385 



sine is incorporated into both nucleic acid-guanine and -adenine. ^^ These data 

 confirm the nutritional findings. Similar data obtained with isotopically la- 

 beled pyrimidines are in agreement with the nutritional evidence that cytidine 

 and uridine are interconvertible and serve as precursors for thymidine and thy- 

 midylic acid. The data further illustrate that similar pathways exist for 



Table 3 

 Purine Requirements of Paramecium 



* Values obtained after iirst transfer. 



Table 4 

 Pyrisodine Reqltirements of Paramecium 



* Values obtained after first transfer. 



purine and pyrimidine utilization in both particle free and particle bearing 

 animals. 



Generally, the requirements for vitamins for particle bearing and particle 

 free animals are similar (table 5). The need for nicotinamide, riboflavin, and 

 thiamine becomes apparent in the second transfer, whereas the requirement for 

 pyrido.xal is evident only after three or four serial subcultures. An absolute 

 requirement for calcium panthentate has not been shown. Some degree of 

 growth, appro.ximating 10 per cent of the control, remains even after several 

 transfers. Biotin and lipoic acid are not required. Particle bearing animals, 



