ANAEROBIC HABITATS 33 



herbivorous animals. In the first case the oxygen has 

 to diffuse over wider distances, wliereas in the intes- 

 tine of herbivores a richer microbial flora may be pres- 

 ent. Due to oxygen absorption by the bacteria a larger 

 accumulation of oxygen may be prevented, even if small 

 amounts constantly flow from the wall to the lumen. 



In general, the regular presence of hydrogen and me- 

 thane in the intestinal gases, both typical end products 

 of incomplete oxidations or of fermentations, together 

 with the regular occurrence of reduction processes in 

 the intestine, seem to indicate rather clearly that there 

 can be no abundant supply of oxygen under natural con- 

 ditions The fact reported by Jahn (1933) that the Eh 

 values in the rat intestine lie well within the anaerobic 

 range is in agreement with this view. According to 

 Campbell (1931) the oxygen tension of the intestinal 

 lumen is practically nil, if food is present. Weighing 

 the entire available evidence, hardly a doubt can remain 

 that the intestinal tract of warm-blooded vertebrates 

 should be regarded as a habitat normally very poor in 

 oxygen, although it is in many cases not purely anaerobic. 



Similar conditions will probably be found in the in- 

 testine of cold-blooded vertebrates and of large inver- 

 tebrates, such as large snails, squids and similar or- 

 ganisms although the lack of oxygen might be not quite 

 so pronounced as in warm-blooded vertebrates. Unfor- 

 tunately no precise data seem to be available. 



One would expect that the intestinal tract of smaller 

 invertebrates should be a habitat more favorable to 

 aerobic life than that of larger animals. One element 

 of evidence pointing in this direction is the observation 

 made by most (although not all) investigators, that the 

 developmental stages of the Leishmanias multiply in 

 culture only under aerobic conditions. These organisms 

 are found normally in the intestinal tract of sandflies. But 

 no generalizations are possible, since other evidence 

 points in the opposite direction. Trager (1934) reports 



