32 RESPIRATION 



The results of Boycott and Haldane with Boycott as subject 

 are shown graphically in Figure 7. It will be seen that, provided 

 that the alveolar oxygen pressure was prevented from falling so 

 low as to cause want of oxygen, the alveolar CO 2 pressure re- 

 mained steady with variations of the barometric pressure from 

 300 to 2800 mm. and corresponding variations in the alveolar 

 CO 2 percentage from 15 to 1.5. 



The daily variations of atmospheric pressure at any one place 

 are not sufficiently great to cause any considerable variations in 

 the alveolar CO 2 percentage, and there are other causes, discussed 

 below, which cause distinct variations in the alveolar CO 2 present. 

 Even, therefore, if we take into consideration the daily variations 

 of atmospheric pressure, the resting alveolar CO 2 pressure is not 

 quite constant at different times in the same individual, and varies 

 considerably in different individuals. 



The differences in the alveolar CO 2 pressure in different indi- 

 viduals, and in different sexes and at different ages, were investi- 

 gated by Miss Fitz Gerald and myself. We obtained the following 

 results from a number of different persons, 17 living at Oxford. 



17 Haldane and FitzGerald, Journ, of Physiol., XXXII, p. 491, 1905. 



