BREATHING IN COMPRESSED AND IN RAREFIED AIR 401 



of the power of secreting 2 into the blood; (3) increase in the erythrocytes 

 and hemoglobin of the blood. The increased alveolar 2 tension is a result 

 of the more rapid breathing brought about by the increased C H of the 

 blood. If no adaptation occurred, the 2 tension at 10,000 feet would be 

 59 mm. and at 15,000 feet, 33.8 mm. Actual observations on men, how- 

 ever, gave at 10,000 feet a tension of 65 mm. and at 15,000 feet, 52 mm. 



The evidence for an increased secretory activity of the pulmonary 

 epithelium depends on observations made by Haldane and his cowork- 

 ers, 33 who found that blood collected from the finger of a man living on 

 a high mountain is brightly arterial, whereas if this same blood is 

 shaken in a flask with alveolar air from the man from whom it was 

 taken, it will become darkly venous. To account for this difference it is 

 believed that the pulmonary epithelium forces 2 into the blood contrary 

 to the laws of diffusion. 



A more exact proof was sought for by comparing the relative amounts 

 of 2 and CO that blood would take up (1) when exposed outside the 

 body and (2) while in the blood vessels. Carbon monoxide has a very 

 great avidity for hemoglobin, so that if blood is shaken in a flask with 

 air containing 0.07 per cent of this gas, colorimetric measurement will 

 show an equal mixture of oxy- and carboxy-hemoglobin. Since carbon 

 monoxide is destroyed with extreme slowness in the body, it is possible 

 by causing a man to breathe a mixture of it in air to determine, in a 

 sample of drawn blood, whether as much carboxy-hemoglobin has been 

 formed as in vitro. If so, the 2 tension in the blood must equal that in 

 the alveoli; if less carboxy-hemoglobin should be formed, it would indi- 

 cate that a higher tension of 2 exists in the blood. This latter is the re- 

 sult which Haldane states he has secured. In one experiment, for ex- 

 ample, when blood was shaken outside the body with 0.04 per cent C0 2 , 

 the amount of carboxy-hemoglobin formed was 31 per cent of the whole 

 hemoglobin. When the same mixture was inhaled for three or four hours 

 the percentage of carboxy-hemoglobin in the blood rose only to 26 per 

 cent, which would correspond to an 2 tension of 25 per cent of an atmos- 

 phere, whereas even at sea level the tension of 2 in the alveolar 

 air can not be above 15 per cent of an atmosphere. 



The constant low tension of 2 in the plasma stimulates the red blood 

 corpuscles and the percentage of hemoglobin to become markedly in- 

 creased after residence for some time in high altitudes. At first this is 

 due to a concentration of the blood by a diminution in plasma, but grad- 

 ually the blood-forming organs become excited and an actual increase 

 in the total amount of hemoglobin occurs. In the light of these facts it 

 is interesting to compare the average number of red corpuscles in the 

 blood of inhabitants living at different altitudes. 



