Physiology 481 



exhaustion of the more readily utilized substrate, and that the bacteria 

 must become adapted to the second sugar before growth is resumed. 



Relationships between growth and pH are fmther complicated by 

 the occasional observation of two "optima" at the end of a given period. 

 Such bimaximal relationships, which remain unexplained, have appeared 

 in bacterized cultures of Stylonychia pustulata (87) and in pure cultures 

 of Tetrahymena pyriforrnis (113, 252) and Chilofvonas Paramecium 



A- 



2-' 



LOG. number/ml 



; / 



<ir/ 



;l— - 





7>/ 



s- 



pH 3.1 (transfer I) 



/ 



pH 3.1 (transfer 2). 



"1 1 1 1 1 r 



50 



1 1 1 r 



100 



DAYS 



Fig. 8. 5. Growth of Astasia loiiga (strain J) in relation to pH of the 

 medium. The curves are based on data of Schoenborn (507). 



(324). The two optima are replaced by one in T. pyrijormis (113) and 

 C. Paramecium, (324) grown in the presence of acetate, and T. pyriformis 

 also shows only one optimum in certain protein and peptone media 

 (113, 114, 115, 252). Additional questions are raised by variations of the 

 apparent optimum with the type of medium (113, 115, 252, 324). This 

 may be the case in bacterized as well as in pure cultures. For instance, 

 Paramecium aurelia has been assigned a pH optimum in certain cases, 

 whereas the fission-rate of this ciliate fed on Serratia marcescens is practi- 

 cally the same between pH 5.9 and 7.7 (438). Growth of Tetrahymena 



