RESPIRATORY METABOLISM 367 



7. THE EFFECT OF NUTRITIVE SUBSTANCES AND OTHER MATERIALS 



The effect of various nutritive substances on Protozoa has been demon- 

 strated by a number of investigators, but the criteria used are usually 

 growth or the accumulation of food reserves, and not respiration. In 

 some cases it is possible to determine that the substance is oxidized 

 directly (e.g., glucose), or that it contributes toward the synthesis of 

 the respiratory enzyme (A. Lwoff, 1933). These data will be dis- 

 cussed below. The effect of various substances on the respiration of 

 Paramecium was studied by Leichsenring (1925), who found that cap- 

 rine, glutamic acid, peptone, and aminoids increased respiration 12-18 

 percent; that glycocoU and succinic acid increased respiration 8-9 per- 

 cent; and that tyrosine and cystine produced little effect. Lactose gave 

 an increase of 16 percent, and other sugars and polysaccharides gave in- 

 creases of 3-10 percent. Thyroxin gave an increase of 13 percent. No 

 explanation was made of the mechanism of these effects. 



Mast, Pace, and Mast (1936) found that Chilomonas grew well, 

 formed considerable starch but little fat, and consumed 0.17 mm^ of O2 

 per 10,000 organisms per hour, in a solution of MgSO^, NH^Cl, 

 K2HPO4, Na-acetate, and silicon. When sulphur was omitted, the starch 

 remained constant, fat accumulated, Oo consumption decreased, and the 

 animals finally died. When acetate was omitted, the organisms decreased 

 in size, starch and fat decreased, and O, consumption decreased to 0.07 

 mmY10,000/hour. When both sulphur and acetate were omitted, starch 

 decreased to zero, fat accumulated, Oo consumption decreased, and the 

 organisms died. These authors conclude that starch is normally changed 

 to fat, that sulphur induces oxidation of fat, thereby increasing respira- 

 tion and preventing accumulation of fat, and that fat oxidation is 

 probably associated with a cystine-cysteine mechanism (see glutathione, 

 below). Mast and Pace (1937) reported a 25 percent increase in res- 

 piration of Chilomonas when Na^SiOg was added to inorganic media. 

 This was supposedly caused by the catalytic action of Si on organic 

 syntheses. 



8. EVOLUTION OF GASES OTHER THAN COg 



The possibility that Protozoa evolve gases other than CO2 was first 

 shown by Cook (1932) for the flagellates of termites [Termopsis neva- 

 densis). A gas which was not absorbable by hydroxide was evolved by 



