36 



ANA EROIilC BA JUT ATS 



that almost any parasite should be able to secure all the 

 oxygen it needs. 



Little information is available concerning the tissues 

 of invertebrates. Campbell (1931) has collected some 

 data on the oxygen tension under the chitin of various 

 species of insects. The values vary from 2 to 18 per 

 cent of that found in a normal atmosphere. 



In bulky animals lacking a circulatory system the oxy- 

 gen tension of the deeper layers of tissues must be zero 

 or nearly zero. As Krogh (1916) pointed out, the 

 supplying of oxygen to the deeper tissue layers is diffi- 

 cult ill this and in similar cases, since the animals depend 

 entirely on the diffusion of oxygen from the surface. 

 Hence only the superficial cell layers receive an ample 

 supply of oxygen, little or none at all reaches the 

 deeper layers. The latter, therefore, must have a more 

 or less pronounced anaerobic metabolism. It is obvious 

 that any parasite that may be found in such tissues will 

 have to lead an anaerobic life. 



TABLE 7 

 Gas Tension in Normal Urine of Man. 



In so far as body secretions are concerned, little re- 

 liable information is available. In urine (Table 7) a 

 moderate amount of oxygen is always present. Less 

 oxygen occurs in concentrated than in dilute urine. 



The determination of oxygen in other secretions, like 

 milk or bile, presents difficulties because this gas has 

 a tendency to disappear rapidly in these fluids. An ex- 

 planation for this phenomenon seems not yet to have 

 been offered. It is obvious that data on specimens that 



