430 Physiology 



TABLE 8. 1. CONSTITUENTS OF CULTURE MEDIA FOR THE 

 COLORLESS PHYTOFLAGELLATE, CHILOMONAS PARAMECIUM, 

 AND THE CILIATE, TETRAHYMENA PYRIFORMIS, STRAIN E (121) 



(In addition to the listed components, various trace elements are present as impurities.) 



terial for studying animal metabolism under conditions controllable to a 

 degree not attained with tissues of higher animals. In addition, precise 

 control of the food supply favors use of these organisms in the search for 

 new vitamins, as in the discovery of protogen (540), as well as in micro- 

 biological assays of known growth-factors (230, 579) and amino acids 

 (494). To the parasitologist and the pathologist, parasitic Protozoa in 

 pure cultures offer unique opportunities for correlating metabolic activ- 

 ities of parasites with susceptibilities to chemotherapeutic agents and with 

 reactions of the host's tissues to infections. To the explorer, these organ- 

 isms extend a challenge to trace nutritional evolution from the possibly 

 complete synthesis of needed vitamins to an essentially complete depend- 

 ence upon external sources. Did plant-like Protozoa suddenly become 

 "animals," with wholesale loss of synthetic abilities, or did they lose their 

 original abilities one by one as evolution tempted them toward the animal 

 kingdom? Or have the phytoflagellates arisen from more animal-like Pro- 

 tozoa, acquiring in their evolution various synthetic powers unknown to 

 their ancestors? 



General types of nutrition 



For many years, general types of nutrition were classified merely as 

 autotrophic (or holophytic), saprozoic, and holozoic, the last two repre- 

 senting varieties of heterotrophic nutrition. By definition, autotrophs 

 could grow in inorganic media while heterotrophs required organic foods. 

 With the exception of saprozoic types. Protozoa probably are not limited 



