502 FOOD REQUIREMENTS 



range for a number of species (for reviews, see Loefer, 1935c; D. F. 

 Johnson, 1935a). More recently, similar investigations have been carried 

 out with bacteria-free material. 



Dusi (1930) has shown that each of six species of Euglena has a 

 characteristic pH range in certain media, and that the optimum varies 

 somewhat for the different species. Jahn (1931), using quantitative 

 methods, has studied that pH relationships of E. gracilis in detail, and 

 similar relationships have been determined for E. anabaena and E. deses 

 (Hall, 1933a) and for two species of Astasia (Schoenborn, 1936). 

 Among the Cryptomonadida and Phytomonadida, the pH-growth rela- 

 tionships of Chilomonas Paramecium, Chlorogonium elongatum, and C. 

 euchlorum have been investigated by Loefer (1935c). Growth of the 

 two phytomonads, with an optimum slightly above pH 7.0, was more 

 or less comparable to that of several Euglenidae; C. Paramecium, on the 

 other hand, showed a bimaximal pH-growth curve with peaks at pH 

 4.9 and 7.0 and an intermediate low point at pH 6.0. 



Relationships between growth and pH have also been determined for 

 several ciliates. Elliott (1933, 1935b) has described the pW ranges and 

 optima for Colpidium campylum and C. striatum, and has pointed out 

 that the pH relationships vary with the type of medium. In one peptone 

 medium (Difco tryptone) a bimodal curve, with peaks at pH 5.5 and 

 7.5, was noted; in certain other peptone media, a unimaximal pH-growth 

 curve was observed. The addition of sodium acetate or a carbohydrate 

 (e.g., maltose) to tryptone medium changed the shape of the curve from 

 bimaximal to unimaximal. The extent of the pH range also varied with 

 the type of medium. D. F. Johnson ( 1935a) , in similar fashion, has com- 

 pared the pH-growth curves of Glaucoma ficaria and G. piriformis in dif- 

 ferent types of media. Appreciable differences between the two species 

 were noted, and the pH range and general form of the growth curves 

 were found to vary with the type of medium, much as in Colpidium. 

 More recently, Loefer (1938a) has studied the growth rate and general 

 morphology of Paramecium hursaria in relation to the pH of the medium. 

 Conditions known to be optimal for the symbiotic Chorella (Loefer, 

 1936a) did not coincide with those most favorable to the growth of 

 P. hursaria containing the algae. The pH optimum for the ciliate was 

 approximately 6.8, and growth occurred within the range 4.9 to about 

 7.8. The size of the ciliates varied with the pH, but independently of 

 the growth rate. 



