Soldo : Axenic Culture of Paramecium 



381 



Purification of the protein factor and subsequent analysis led to the qualitative 

 identification of 16 amino acids. The nutritional role of this protein has not 

 been satisfactorily explained. In table 1 is given the composition of a typical 

 medium which supports the growth of most strains of Paramecium. 



Axenic cultivation of X-bearing Paramecium. Lambda particles were dis- 

 covered in the cytoplasm of stock 299X of P. aurelia by Schneller, in 1958.^^ 

 She noted that animals containing these particles possessed the ability to kill 

 sensitive or particle free animals when members of the appropriate types were 

 placed in the same container. In this respect, this particle-protozoan system 

 is similar to the well known k system.^^ 



Table 1 

 Axenic Medium for Paramecium 



* Components known to be absolute requirements for the growth of one or more species 

 of Paramecium. 



t For preparation see (9). May be replaced by Pea factor for P. caudatum (14). 



Efforts to cultivate X-bearing animals in media used for the growth of parti- 

 cle free strains were unsuccessful. It was necessary to supplement a crude 

 medium consisting of proteose peptone, a dialyzable component of hot water 

 extract of Baker's yeast and salts, with Edamine S, an enzymatic digest of 

 lactalbumin.'^ This medium supported the growth of the protozoans and main- 

 tenance of the particles through serial subcultures for a period of 2 years. 



Particles of axenically cultivated animals number several hundred per cell, 

 contain RNA, little or no DNA, and are similar in size to the bacterium, 

 Escherichia coli.^^ They are gram-negative and may be stained with most 

 bacteriological dyes. Examination under phase microscope reveals a rod or 

 diplorod type structure. A furrow which divides the particle into almost 



