FOOD REQUIREMENTS 481 



been added to salt solutions comparable, except for the omission of 

 inorganic nitrogen, to the media used for photoautotrophic nutrition. 



Photometatrophic Nutrition 



Photometatrophic nutrition can be carried on by all of the chlorophyll- 

 bearing flagellates which have been established in pure culture. Certain 

 species, such as E. p/sdformh (Dusi, 1933b), may prove to be obligate 

 photometatrophs, although recent observations (Dusi, 1939) indicate 

 that E. p/safonms should not be so classified. Peptones of one type or 

 another have usually furnished the food supply, and in at least a few 

 cases a solution of peptone in distilled water has supported growth. In 

 addition to peptones, gelatin (Hall, 1938b) may also support growth, 

 and certain species are known to produce proteolytic enzymes (Mainx, 

 1928; Jahn, 1931; Hall, 1937b). Many of the flagellates grow well on 

 agar slants, provided the agar is enriched with a suitable peptone and 

 sometimes with an additional source of carbon; such cultures are con- 

 venient for the maintenance of laboratory stocks. 



Although various peptone media are satisfactory for all the species 

 which have been studied, growth may be accelerated by the addition of 

 salts of certain fatty acids, various carbohydrates, and several alcohols. 

 Acceleration of growth by carbohydrates has been noted in E. gracilis 

 (Jahn, 1935b) and in two species of Chlorogonium (Loefer, 1935a). 

 Fermentation of dextrose by E. proxima was reported by Glaser and 

 Coria ( 1930, 1935a) , but other workers have failed to note such changes 

 in cultures of Euglenidae. Furthermore, Loefer (1938b), using Bene- 

 dict's colorimetric method, failed to detect utilization of dextrose by 

 C. elongatum and C. euchlorum, in spite of the accelerating effect on 

 growth. Acceleration of growth by ethyl alcohol has been reported by 

 Loefer and Hall (1936) in E. deses and E. gracilis, and similar effects 

 of several alcohols on the latter species have been described by Provasoli 

 (1938c). Acceleration of growth by fatty acids, in cultures exposed to 

 light, has been reported for E. gracilis (Jahn, 1935d) and E. stellata 

 (Hall, 1937d). Furthermore, macroscopic observations on cultures in 

 various stock-culture media have indicated such effects in approximately 

 thirty species maintained in our laboratory. However, most of the quanti- 

 tative studies on carbon sources have been based upon cultures main- 



