CHAPTER II 



ANAEROBIC HABITATS 



Most habitats in which, because of lack of oxygen, ani- 

 mals will be forced to gain their energy predominantly 

 or exclusively through fermentations are aquatic or 

 semi-aquatic. (We consider as semi-aquatic such "mil- 

 ieux" as the intestinal contents.) Oxygen-poor or oxygen- 

 free terrestrial habitats are relatively rare. 



1. SOILS 



The oxygen content of soils seems in most cases to be 

 too high to markedly impair the aerobic functions of the 

 soil fauna. However, nearly anaerobic conditions last- 

 ing for several months were recently described by Boyn- 

 ton and Eeuther (1938) for two orchard soils. 



In swamplands low oxygen contents that may be of 

 biological significance are encountered (Table 1). 



TABLE 1 



Composition of the Gas Mixture ix Soils Under Various Conditions 



(According to Waksman, 1932). 



The figures are averages of several determinations in per cent. 



The oxygen tension of a soil may be quite different 

 before and after a rain. A saturation of the upper soil 

 layers with water will impair the exchange between the 

 atmosphere and the soil gases below the water-filled zone. 

 The oxygen demand of the soil fauna and flora, as Avell as 



