DIFFERENCES IN ANAEROB. FUNCTIONS 269 



media with a range of potentials varying from -330 to 

 +227 mv. and found the maximum survival at -81 mv. 

 Hutchinson, Deevey and Wollack (1939) investigated 

 the potential of lake waters, about 0.5 m. above the mud, 

 in cases where the latter harbored different chironomids. 

 If the winter had a potential above +400 mv. Tanytarsus 

 was i^resent; if the potential was below +300 the fauna 

 was of a true CJiirouomus.tjVG', while Endochironomus, 

 or mesotrophic Chironomus characterized the interme- 

 diate range. The authors point out, however, that their 

 study has no direct bearing on the question of the in- 

 fluence of the jDotentials on the respiratory physiology of 

 mud-dwellers, but "that the relationship here established 

 is primarily of typological interest, indicating the re- 

 ducing power of the mud as it affects the open water." 

 In the mud itself, i.e., in the immediate surroundings of 

 the animals, lower potentials must be expected, but 

 these seem to have been measured in only one case, in 

 which a value of +150 mv. w^as found. 



The last question to be discussed is whether the intra- 

 cellular oxidation-reduction potential varies with the 

 oxj'gen content of the medium and whether there are dif- 

 ferences in this respect betw^een animals that are purely 

 or predominantly aerobic and those that are adapted to 

 a predominantly anaerobic life. The intensity of the 

 intra-cellular potential is usually expressed by the rH 

 va-ue, that is, by the negative logarithm of the hypotheti- 

 cal hydrogen pressure in equilibrium with the oxidation- 

 reduction system in question; this mode of expressing 

 the potential will be used in the following discussion. 



Needham and Needham (1926) observed that the nor- 

 mally aerobic Amoeba proieus maintains an unchanged 

 rH of about 18 in water saturated with air, oxygen or 

 hydrogen. With Nyctotherus cordiformis, on the con- 

 trary, which occurs in the presumably oxygen-poor in- 

 testine of frogs, the rH was between 19 and 20 under 



