490 FOOD REQUIREMENTS 



sary constituent of media for the growth of E. anabaena and E. gracilis 

 in light. The former has been grown in inorganic media by Dusi and by 

 Hall; the latter, by Dusi and by Hall and Schoenborn. It is obvious, 

 therefore, that the inorganic food requirements of a given species should 

 be satisfied, as a prerequisite to the evaluation of specific growth factors. 



Aneurin, or thiamine {vitamin B^^. — It must be admitted that the 

 facultative photoautotrophs and heteroautotrophs are capable of synthe- 

 sizing aneurin, if this substance is actually essential to the growth 

 of such organisms. Various other Protozoa, however, apparently show a 

 definite need for aneurin, or for one or both of its constituents. 



Among the Cryptomonadida, the thiamine requirements of C. Para- 

 mecium have been investigated by A. Lwoff and Dusi (1937b, 1938a). 

 In their first publication these workers stated that growth of the 

 flagellate in asparagin medium is supported by thiamine, or by thiazole 

 alone. In their later article, they have concluded that for growth in an 

 ammonium acetate medium, thiamine can be replaced by thiazole and 

 pyrimidine, but not by either one separately. Without the growth factor, 

 growth in the control medium was always negative. Recently, A. Lwoff 

 and Dusi (1938b, 1938c) have shown that these substances are not 

 specific; so far as C. Paramecium is concerned, several thiazoles and 

 pyrimidines are satisfactory for growth. 



In the Euglenida, the existence of photoautotrophic species (£. gracilis, 

 and others) and the occurrence of heteroautotrophic nutrition {Astasia 

 sp., Schoenborn, 1938, 1940) seem to belie a need for thiamine in cer- 

 tain species. Furthermore, Elliott (1937a) observed no accelerating ef- 

 fect of this substance on the growth of E. gracilis in light. However, it 

 has been assumed that such flagellates are capable of synthesizing thia- 

 mine in light, and this hypothesis receives indirect support from re- 

 ports that the growth of E. gracilis in darkness is possible in an asparagin 

 and acetate medium only when thiamine (Lwoff and Dusi, 1937c) or 

 pyrimidine (Lwoff and Dusi, 1938a) is present. On the other hand, 

 Dusi (1939) has concluded that E. pisciformis requires such a growth 

 factor even in light, since an asparagin medium containing thiamine (or 

 both thiazole and pyrimidine) supported growth, while the same medium 

 without a growth factor was unsatisfactory. 



In this connection, it has been noted (Hall, 1938b) that growth 

 of E. anabaena in light is little, if any, better in an asparagin medium 



