PHYSIOLOGY 117 



the smaller the size of body and the more elaborate the contractile 

 vacuole system, the organisms suffer the less the lack of oxygen in 

 the water, since the removal of catabolic products depends upon these 

 factors. 



The variety of habitats and results of artificial cultivations of 

 various Protozoa indicate clearly that the oxygen requirements vary 

 a great deal among different forms. Attempts were made in recent 

 years to determine the oxygen requirement of Protozoa. The results 

 of the observations are not always convincing. The oxygen consump- 

 tion of Paramecium is said, according to Lund (1918) and Amberson 

 (1928), to be fairly constant over a wide range of oxygen concentra- 

 tion. Specht (1934) found the measurements of the oxygen con- 

 sumption and carbon dioxide production in Spirostomum ambiguum 

 vary because of the presence of a base produced by the organism. 

 Soule (1925) observed in the cultural tubes of Trypanosoma lewisi 

 and Leishmania tropica, the oxygen contained in about 100 c.c. of 

 air of the test tube is used up in about 12 and 6 days respectively. 

 A single Paramedian caudatum is said to consume in one hour at 

 21°C. from 0.0052 c.c. (Kalmus) to 0.00049 c.c. (Howland and Bern- 

 stein) of oxygen. The oxygen consumption of this ciliate in heavy 

 suspensions (3X10 3 to 301 X10 3 in 3 c.c.) and associated bacteria, 

 ranged, according to Gremsbergen and Reynaerts-De Pont (1952), 

 from 1000 to 4000 nM 3 per hour per million individuals at 23.5°C. 

 The two observers considered that P. caudatum possesses a typical 

 cytochrome-oxidase system. Amoeba proteus, according to Hulpieu 

 (1930), succumbs slowly when the amount of oxygen in water is less 

 than 0.005 per cent and also in excess, which latter confirms Putter's 

 observation on Spirostomum. According to Clark (1942), a normal 

 Amoeba proteus consumes 1.4 X10~ 3 mm 3 of oxygen per hour, while 

 an enucleated amoeba only 0.2X10 -3 mm 3 . He suggests that "the 

 oxygen-carriers concerned with 70 per cent of the normal respiration 

 of an amoeba are related in some way to the presence of the nu- 

 cleus." In Pelomyxa caroUnensis, the rate of oxygen consumption at 

 25°C. was found by Pace and Belda (1944) to be 0.244+0.028 mm 3 

 per hour per mm 3 cell substance and does not differ greatly from 

 that of Amoeba proteus and Actinosphaervum eichhorni. The tem- 

 perature coefficient for the rate of respiration is nearly the same as 

 that in Paramecium, varying from 1.7 at 15-25°C. to 2.1 at 25-35°C. 

 Pace and Kimura (1946) further note in Pelomyxa caroUnensis that 

 carbohydrate metabolism is greater at higher than at lower tem- 

 perature and that a cytochrome-cytochrome oxidase system is the 

 mechanism chiefly involved in oxidation of carbohydrate. 



