Physiology 439 



of pyridoxal and riboflavin (207). In addition, growth of Tetrahymena 

 pyriformis on C. Paramecium and on Polytoma ocellatum in similar cul- 

 ture media (182) suggests that these flagellates are able to synthesize a 

 variety of vitamins needed by the ciliate. Therefore, it may be assumed, 

 in the absence of evidence to the contrary, that metabolic activities of the 

 phytoflagellates involve essentially the same vitamins as do those of the 

 higher Protozoa. Under favorable conditions, which must include a 

 medium satisfying essential mineral requirements, some species may be 

 able to synthesize all of their needed vitamins. Present indications, that 

 certain other phytoflagellates cannot synthesize at least one or two vita- 

 mins from simple materials, raise interesting possibilities. Perhaps it will 

 be feasible, in this group, to trace a series of stages in the development of 

 multiple vitamin requirements (or multiple losses in synthetic powers) as 

 represented by ciliates, for example. As the scope of the pure-culture tech- 

 niques is broadened, the ability to visualize vitamin requirements on a 

 taxonomic framework may prove very interesting — possibly to the extent 

 of furnishing clues to the phylogeny of the higher Protozoa. From the 

 practical standpoint, the determination of vitamin requirements for many 

 different Protozoa may reveal unsuspected new vitamins and may also 

 furnish additional tools for luicrobiological assays. Both possibilities have 

 already been realized to a limited extent. 



Some information on vitamin requirements is now at hand for a num- 

 ber of species (Table 8. 3). Although the present data may be definitive 

 for a few phytoflagellates, this is far from true for nearly all of the other 

 Protozoa which have been investigated. 



Thiamine. This vitamin is an absolute requirement for certain strains 

 of ciliates and parasitic flagellates and probably for malarial parasites. 

 The case of Chilomonas Paramecium is still puzzling. Certain strains 

 apparently require either thiamine or its thiazole and pyrimidine com- 

 ponents, while others have been grown in all-glass vessels without added 

 thiamine on acetate as a substrate (73, 390). Under such conditions, sup- 

 plementary thiamine markedly increases growth on acetate and becomes 

 essential instead of stimulatory when pyruvate is substituted for acetate 

 (73). Thiamine is stimulatory for Polytoma obtusuyn and P. uvella in 

 simple media, although both will grow without the added vitamin (348). 

 In the same types of media, certain other colorless phytomonads need 

 thiazole or both the pyrimidine and thiazole components of thiamine 

 (Table 8. 3). Several substituted thiazoles and pyrimidine also are active 

 for Polytomella caeca and Chilomonas Paramecium (348). In addition, 

 heavy growth of Euglena gracilis var. bacillaris, in an amino acid and 

 inorganic salt medium containing vitamin Bjo, depends upon an adequate 

 concentration of thiamine (230). 



Riboflavin. Earlier reports of growth-acceleration in ciliates (120, 181, 

 183, 283) were soon followed by evidence that this vitamin is essential for 



