C12 Professor Joseph Barcroft [June 0, 



stood at only 450 mm., or about 18 in. Shortly a more mature boy 

 appeared — perhaps seventeen or eighteen years of age — his load was 

 about 100 lbs. To understand these feats, it must be remembered 

 that exercise may be of two kinds, spasmodic or continuous. In the 

 case of continuous exercise, such as that of long-distance running, 

 the subject must maintain an approximate equilibrium between the 

 oxygen which he uses and that which he absorbs. His oxygen 

 account must, so to speak, balance approximately at any given time. 

 In the case of spasmodic exercise it is otherwise. If the subject is 

 prepared for the exercise to cease after a very short time, he may 

 expend oxygen at a greater rate than he takes it in, and thus over- 

 draw his oxygen account. A limit is, however, set to the overdraft, 

 and when that limit is reached he must rest till his oxygen account 

 has righted itself. This formed the subject of a most interesting 

 investigation carried out by Dr. Lupton recently in the laboratory of 

 Prof. A. Y. Hill. The porters in the old Spanish mine raise their 

 loads by a series of spasmodic efforts, each of which is followed by a 

 rest of considerable length accompanied by great respiratory distress. 



Of the means by which the body acclimatises itself to oxygen 

 want, real or alleged, we investigated the following :— 



1. Secretion of Oxygen by the Pulmonary Epithelium. — Numerous 

 direct estimations were made of the oxygen pressure in the arterial 

 blood, and in the alveolar air. The two usually came out within 

 two or three millimetres of one another, which is approximately the 

 experimental error of the method. Such a coincidence can only 

 mean that the oxygen passes into the blood by a process of diffusion 

 through the very attenuated partition of epithelium which separates 

 the air from the blood in the lung. Thus the view that the lung 

 could enable the body gradually to overcome the effects of altitude 

 by creating a sort of forced draught and maintaining the oxygen 

 pressure in the blood at its sea-level value is unfounded. 



However, the blood as it leaves the lung must contain appreciably 

 less oxygen than its hemoglobin would normally absorb. It is, to 

 use the American phrase, unsaturated to a considerable degree. 

 Such blood, of course, would lack the bright scarlet colour of true 

 arterial blood. The actual colour of the biood as withdrawn from 

 the radial artery entirely bore out this view ; as it flowed into the 

 syringe it was of a dull red colour, often verging on chocolate, and 

 in the case of the natives was 82-86 per cent, saturated with oxygen, 

 instead of 95-96 per cent, as at the sea level. 



Curves giving the relation between the percentage saturation of 

 the blood and the partial pressure of oxygen in lungs at Lima and 

 Cerro de Pasco for different members of the party are shown in 

 Fig. 1, from which it is apparent that at high altitudes the partial 

 pressure required to secure a percentage saturation sufficient for life 

 decreases considerably. 



The establishmeunt of the fact that life can be supported with 



