Respiration and Metabolism 



249 



at high tensions is highest for animals maintained at 4° C. and lowest for those 

 kept at 30° C, the rate of oxygen consumption is the same for all when 

 measured at 35-40 mm. Hg oxygen tension (Fig. 56). The oxygen tension 

 necessary to maintain a constant body temperature of 37° in mice at 30° 

 C. air temperature is 64 mm. I Ig; at 20° it is 97 mm. Hg, and at 4° it is 155 

 mm. Hg. At lower tensions the body temperature declines. 



Fig. 57. Curves showing the least tolerable oxygen concentration as a function of pH 

 for fish: (1) goldfish, (2) yellow perch, (3) and (4) bluntnose minnow, (5) steel- 

 colored minnow, (6) bluegill. Temperatures 18-25° C. From Wiebe et al.™' 



Effect of pH on Minimum Tension. The minimum oxygen concentration 

 which can be tolerated may vary with the pH, but whether this is an effect 

 of its respiratory stimulating powers or of the ability of the organism to extract 

 oxygen within a limited pH range is uncertain. Probably the respiratory stimu- 



