FOOD REQUIREMENTS 507 



mildly toxic in light, while oxalate exerted no effect in darkness and a 

 slight acceleration in light. Hall (1937d) observed also that in E. stel- 

 lata tolerance to concentrations of acetate above 0.2 percent was much 

 less in light than in darkness. Furthermore, Jahn (1936b) has obtained 

 some evidence that intensity of light may influence the effects of carbo- 

 hydrates on the growth of E. gracilis in an inorganic medium. Another 

 instance involving light relationships is the effect of plant "hormones" 

 on E. gracilis, in which Elliott (1937b) has shown that growth is ac- 

 celerated in light, but not in darkness. 



Acclimatization 



Acclimatization of Protozoa to various experimental conditions has 

 been reported in many instances, ranging from acclimatization to toxic 

 chemicals to the development of resistance to antibodies. A few cases 

 have been described in bacteria-free cultures of free-living species. Such 

 a process may occasionally be involved in the establishment of pure cul- 

 tures, as reported by Elliott (1933) for Colpidium striatum and by 

 Johnson (1935a) for Glaucoma fcaria. More recently, Loefer (1938c) 

 has studied the acclimatization of several species (C campylum, G. piri- 

 formis, Chlorogonium euchlorum, Euglena gracilis, and Astasia sp.) to 

 progressively increased salt concentrations. E. gracilis developed no ap- 

 preciable tolerance, but, after a series of transfers, the other species 

 all showed the ability to grow in salt concentrations which were lethal 

 in the initial exposures. The salinity finally tolerated by C. campylum 

 was higher than that of ordinary sea water. Further investigations on 

 acclimatization should prove interesting, and may throw some light on 

 various experimental results which at present seem very puzzling. 



Literature Cited 



No attempt has been made to include all the literature on bacteria-free 

 cultures of Protozoa. Among the papers cited, those which contain good 

 bibliographies are indicated by an asterisk. 



Andrews, J., and T. von Brand. 1938. Quantitative studies on glucose con- 

 sumption by Trichomonas foetus. Amer. J. Hyg., 28: 138-47. 



Bond, R. M. 1933. A contribution to the study of the natural food cycle in 

 aquatic environments. Bull. Bingham oceanogr. Coll. 4 (Art. 4), 89 pp. 



Brand, T. von. 1938.* The metabolism of pathogenic trypanosomes and the 

 carbohydrate metabolism of their hosts. Quart. Rev. Biol., 13: 41-50. 



