Mastigophora 57 



(1935), and Johnson (1936) show that growth of various species of flag- 

 ellates and ciliates in bacteria-free cultures is influenced to a marked 

 degree by the pH of the medium. The literature on this subject has been 

 reviewed by Loefer (1935). Not only is there a direct relationship 

 between pH and growth in the simpler media, but there are also indirect 

 relationships to be considered. For example, it is known (Elliott, 1935a) 

 that sodium acetate accelerates growth of Colpidium in a medium near 

 pH 7.0, but is decidedly toxic in media below pH 5.5, although the latter 

 pH is near the optimum for growth of the ciliate in acetate-free media. 

 Observations in progress on several species of Euglena indicate that 

 similar relationships hold for the green flagellates. Elliott (1935) has 

 noted a similar relationship between pH of the medium and the accel- 

 erating effects of carbohydrates on growth of Colpidium. Near the neu- 

 tral point, little or no acceleration was observed with certain carbo- 

 hydrates, whereas in the acid range growth was decidedly stimulated by 

 the same carbohydrates. 



The concentration of both organic and inorganic constituents of the 

 medium may also have an important bearing on the maintenance of 

 bacteria-free cultures, as indicated by the observations of Cailleau 

 (1933a), Elliott (1935a), Loefer (1936a), and Johnson (1936). It is 

 known that the addition of various substances — such as dextrose and 

 other carbohydrates, sodium acetate and other salts of the lower fatty 

 acids, yeast extract, etc. — to media listed above will increase the growth 

 of a number of species of Protozoa. Our observations show that the 

 factor of concentrations is important in the determination of such acceler- 

 ating effects, since an amount in excess of the optimal concentration may 

 even inhibit growth of the Protozoa. This question has been discussed in 

 detail by Loefer (1936a). 



References 



For the culture of many colorless and pale green flagellates see p. 177. 

 Order Chrysomonadida, Family Ochromonadidae 

 For the culture of Ochromonas see p. 62. 



Bibliography 



Cailleau, R. 1933. Culture d'Acanthamoeba castellani en milieu liquide. C. R. 

 Soc. Biol. 113:990. 



1933a. Culture d'Acanthamoeba castellani sur milieu peptone. Action sur 



les glucides. Ibid. 114:474. 



Dusi, H. 1930. La nutrition autotrophe d'Euglena gracilis Klebs aux depens de 

 quelques azotes inorganiques. Ibid. 104:662. 



1930a. Les limites de la concentration en ions H pour la culture de quel- 

 ques Euglenes. Ibid. 104:734. 



1933. Recherches sur la nutrition de quelques Euglenes. 



I. Euglena gracilis. Ann. Inst. Pasteur 50:550. 

 1933a. Recherches sur la nutrition de quelques Euglenes. 



