Respiration and Metabolisni 



247 



TABLE 43. CRITICAL OXYGEN TENS10?^S 



more active perch require twice this concentration. Conversely, the frog— and 

 this is not indicated in any correlation of critical tensions— has been claimed to 

 get along for 24 hours in the absence of oxygen. -^^ 



The response of individual tissues to decreasing oxygen tensions need not 

 be the same as that of the entire organism. Isolated frog muscle, for example, 

 shows a constant oxygen uptake when the partial pressure of oxygen is reduced 

 from 760 mm. to 0.5-2.0 mm. Hg.^^'"' 



Blood Pigments and Oxygen Tension. An important factor in the ability 

 of an organism to regulate oxygen consumption and thereby remain physiolog- 

 ically aloof from the depressive effect of reduced tension is the affinity of the 

 blood pigments for oxygen, and particularly the saturation tension Ct^„t) and 

 tension at half-saturation (ti/^Mit), as well as the effects of carbon dioxide, pfl, 

 and temperature on these blood oxygen levels. This is discussed at length in 

 connection with blood pigments (see Chapter 9). However, some correla- 

 tions are in order here. 



