METHODS OF INVESTIGATION 17 



microorganism flora and fauna of such a medium rapidly 

 exhausts all the molecular oxygen. This method has the 

 advantage of keeping the test organisms in semi-natural 

 environments. The main disadvantage is that the proc- 

 esses occurring in the ooze are beyond control. Often 

 hydrogen sulfide is produced and many organisms seem 

 to succumb to this gas rather than to the lack of oxygen. 



Anaerobic conditions can also be produced by absorb- 

 ing oxygen by chemical methods, e.g., by alkaline solu- 

 tion of pyrogallol. When fluid media are to be deoxygen- 

 ated in this manner the surface/volume ratio of the cul- 

 ture fluid should always be high enough. Snyder and 

 Meleney (1943), in their work on the anaerobic culture of 

 Endamoeba histolytica, inserted alkaline pyrogallate 

 sponges above 1 cc. of culture fluid in tubes of 16 mm. 

 diameter. For animals that can be kept in a gaseous 

 atmosphere any type of container that can be hermetical- 

 ly sealed and in which the organisms can be kept from 

 direct contact with the absorbing fluid can be employed. 

 Anaerobic culture jars as used in bacteriology are often 

 very satisfactory, but in many cases simple improvised 

 containers will be just as good. 



The advantage of the chemical absorption of oxygen 

 is that one can judge accurately the onset and the de- 

 gree of the anoxic conditions. The chief drawback is 

 that at least some organisms seem to be sensitive to an 

 abrupt transition from an aerobic to a strictly anaerobic 

 environment. 



(c) Replacement of oxygen with an 

 inert gas. To replace the oxygen by hydrogen 

 or nitrogen is one of the safest and most rapid ways of 

 establishing strictly anaerobic conditions. The advan- 

 tages and disadvantages are the same as those mentioned 

 above for chemical absorption. 



No experimental difficulties are experienced with ani- 

 mals living normally in air. The latter is simply replaced 

 by a stream of inert gas. Naturally, care must be taken 



