16 METflODH OF IXVK^^TraATrON 



(b) A b s o r }) t i o II o f o x y g o ii . The oxygen 

 present in the medium is absorbed either by living organ- 

 isms or by chemicals. In the former case the experi- 

 mental animals are simply put into tightly closed con- 

 tainers and their own oxygen consumption gradually ex- 

 hausts the oxygen present. The advantage of this method 

 is that anaerobic conditions are established gradually; 

 the main disadvantage is that one can never be quite 

 certain just exactly at what point all the oxygen has 

 disappeared. An approximate idea of the degree of oxy- 

 gen deiDletion can, however, be obtained by analyzing, 

 after various time intervals, the oxygen remaining in 

 comparable vessels containing the same number of organ- 

 isms {cf. von Brand, 1927). 



Occasionally the oxygen consumption of organisms 

 other than those to be tested has been employed for sim- 

 ilar purposes. Faure-Fremiet, Leon, Mayer and Plante- 

 fol (1929) used, for example, germinating bean seedlings 

 kept in the dark to exhaust the oxygen in solutions in 

 which the anaerobic survival of Paramaecium was studied. 

 Such a procedure may be more dangerous than the use 

 of the test organisms themselves. If the latter do not 

 consume the last traces of oxygen, they at least remove 

 the amount of oxygen which they are able to utilize and 

 that is the important thing. With another organism, 

 there is always a danger that it may cease its oxygen 

 consumption at tensions that are still of significance to 

 the test organisms. In special cases cultures of aerobic 

 bacteria can be used to exhaust the oxygen. Such a pro- 

 cedure, patterned after the original method of Fortner 

 (1928, 1929) was employed by Levitanskaja (1938), for 

 example, in culturing Balantidium coli. 



Anaerobic conditions of significant severity can be es- 

 tablished without difficulty for mud dwellers. Juday 

 (1908) and Lindeman (1942) simply filled containers with 

 the ooze from the bottom of lakes and tightly closed them 

 after the test organisms had been introduced. The mixed 



