260 I'LACJJ OF AXAFh'OH. /A MF/VMiOLI^^M 



tubes which are ovci^ayod mth vaseline may well indi- 

 cate that low oxygen concentrations are not toxic, since 

 a vaseline seal is not perfectly air-tight. Similarly, it is 

 not certain that the culture methods employed for the 

 rumen protozoa excluded the last traces of oxygen. The 

 sapropelic ciliates have never been cultured successfully 

 in the laboratory; they survived only for short periods 

 under the experimental conditions to w^iich they were 

 subjected. As to the sewage protozoa, apparently no 

 attempt has been made so far to study the influence of low 

 oxygen concentrations on them. 



Assuming that there are non-toxic concentrations of 

 oxygen for the organisms just mentioned, a very impor- 

 tant problem which has not yet been tackled is whether 

 these animals are able to consume that oxygen. This 

 problem will be difficult to solve, since it presupposes the 

 establishment of bacteria-free cultures. The view re- 

 cently expressed by Krogli (1941) is of great interest 

 in this connection. He writes: " , . , from the obser- 

 vations on many different animals, from worms and in- 

 sects to diving mammals, the impression remains that 

 the continued provision of quite small and in themselves 

 absolutely insufficient amounts of oxygen is essential for 

 the successful resistance against asphyxiation. ... It 

 may be a more fundamental ])henomenon, perhaps anal- 

 ogous to the necessity of metabolizing a little carbo- 

 hydrate along with fats." The above protozoa should 

 be suitable material on which to test whether Krogh's 

 view applies also to unicellular animals. If such experi- 

 ments should yield positive results the organisms in ques- 

 tion would, strictly speaking, not be true anaerobes. (The 

 setting aside of these organisms in a special group will, 

 nevertheless remain justifiable, since their metabolism 

 would, under any condition, be cha.racterized mainly by 

 anaerobic processes, and since it appears necessary to sep- 

 arate them from typical euryanoxybiotic aero-fermenters 

 which are much less sensitive to the toxic effects of 

 oxygen). 



