RESPIRATORY METABOLISM 363 



the relationship between O. tension and O. consumption in Protozoa 

 will apparently require much more data than is now available. A dis- 

 cussion of the theoretical relationship between oxygen tension and oxygen 

 consumption is given by Marsh (1935). 



For Protozoa, the available evidence indicates that within wide limits 

 O2 tension has little or no effect on the rate of O. consumption for 

 Faramecmm and Colpoda, and that it does have an effect on Spirostomum. 

 Lund (1918a) found that the rate of O^ consumption for Paramecium 

 was independent of O, tension between 0.04 cc. and 2.2 cc. O2 per 

 137 cc. — a 55-fold range. This was determined by placing thick sus- 

 pensions of Paramecium in stoppered bottles and measuring the dis- 

 solved O2 content of the water by the Winkler method, until the animals 

 died. Lund's conclusion was confirmed by Amberson (1928), who 

 placed the organisms in a closed vessel, in contact with an atmosphere 

 of known O, content. By gas analyses he demonstrated a uniform rate 

 of Oo consumption, with Oo partial pressures which varied from 

 50 to 220 mm. Hg, and only a slight decrease (about 20 percent) at 

 pressures as low as 11 mm. Hg. Adolph (1929) found that the O2 

 consumption of Colpoda did not vary significantly with Oo tension 

 between 155 and 750 mm. Hg. In a single experiment at 4-8 mm. Hg, 

 O2 consumption decreased to 31 percent of its previous value. However, 

 Adolph did find that low Oo tension (40 mm.) was correlated with 

 smaller size of the progeny of cultures. Specht (1935) measured the 

 respiration of Spirostomum in pure oxygen, in air, and in 0.5 percent 

 O2 in N2. He found that O2 consumption in these gases was in the 

 ratio of 151 to 100 to 71, and that COo production was in the ratio of 

 175 to 100 to 70. 



When considering the effect of low Oo tensions on Oo consumption 

 for any of the larger Protozoa, one should consider the Oo tension at 

 various points within the organism as well as at the surface. This can 

 be calculated by the diffusion equations of Harvey (1928) and others, 

 on the assumption that the rates of cyclosis and water exchange are 

 low. The O2 tension at the center of an ellipsoid which is consuming 

 O2 uniformly throughout its substance, will be zero when the shortest 

 radius 



5Dr 



