The acquisition of oxygen by the Hood in the lung 217 



If 5 mm. be allowed, the arterial blood would be saturated to the 

 extent of about 40 / . Now if 50 mm. pressure head in the lung will 

 not suffice for the passage of 3500 c.c. of oxygen per minute, 5 mm. 

 would not suffice for the passage of 350 and it is clear that each of 

 the party must have been using three or four times this amount. If 

 the arterial blood during work at high altitudes contained less oxygen 

 than the mean value for normal venous blood at the sea-level, what 

 would the venous blood contain and what possibility would there be 

 of obtaining a pressure gradient sufficient to transfer the oxygen from 

 the blood to the tissues? At present the diffusion theory fails to 

 answer these questions though it may do so one day. 



On the secretory theory these considerations are explained, for the 

 members of the Pikes Peak expedition (8) found evidence of oxygen 

 secretion living at an altitude of 14,000 feet. They consider that the 

 secretion increased as their residence continued. Further experi- 

 ments are necessary in two directions. Hartridge should extend his 

 series to sustained work, both at low and at high altitudes, and should 

 he find no greater pressure gradient than he has already done, fresh 

 determinations of the diffusion coefficient are required in order to 

 prove that the actual quantities of oxygen used can pass by diffusion 

 through the pulmonary epithelium when driven by a difference of 

 pressure of only a few millimetres between the oxygen in the alveolar 

 air and that in the arterial blood. 



REFERENCES 



(1) Krogh, Skand. Arch.f. Physiol. xxm, pp. 179, 193, 200, 217, 224, 236, 248, 1910. 



(2) Douglas, Journal of Pht/siol. xxxix, p. 453, 1910. 



(3) Douglas and Haldaue, Skand. Arch.f. Physiol. xxv, p. 169, 1910. 



(4) Hartridge, Journal of Physiol. XLIV, p. 1, 1912. 



(5) Hartridge, Royal Soc. Proc. Ser. B, Vol. LXXXVI, p. 128. 



(6) Hartridge, Journal of Physiol. XLIV, p. 22, 1912. 



(7) Hartridge, Ibid, XLV, p. 170, 1912. 



(8) See Douglas, Haldane, Henderson and Schneider, Phil. Trans. Ser. B, ccin, p. 310. 



