IQO 



RESPIRATION 



It has already been shown in Chapters VI and VII that until 

 the oxygen pressure of the inspired air is lowered by about a third, 

 or that of the alveolar air to about half (i.e., from about lOO mm. 

 to 50 mm.) there is no marked immediate increase in the breath- 

 ing. The effect on the respiratory center of the very distinct degree 



Attihide 

 750 700 650 600 560 500 450 400 550 ZOO 2SO 20O 



Gas pressure 

 ■mm.cf 800 

 mercwy 



in Ft 



120 



too 



300 7SO 100 650 6O0 550 500 4SO 400 3SO 300 250 20O 

 Atmospheric pressure in mm. of mercury. 



, Figure 57- 

 Alveolar gas pressures in relation to barometric pressure or altitude. 



of anoxaemia which is undoubtedly produced, in the manner ex- 

 plained in Chapter VII, is almost entirely masked by the con- 

 trary effect due to extra washing out of CO2 and consequent 

 lowering of the Ph in the arterial blood. But if exposure to the 

 lowered oxygen pressure is continued, not merely for perhaps an 

 hour, but for days or weeks, there is a quite marked increase in 



