690 PHYSIOLOGY OF RESPIRATION. 



such conditions gradually become acclimated, and Haldane believes that the 

 essential factor in the acclimatization consists in the assumption of a secretory 

 activity for oxygen upon the part of the lungs. His reason for this view is the 

 discovery that the oxygen-pressure in the arterial blood under these conditions 

 is greater than the oxygen-pressure in the alveolar air. The oxygen-pressure 

 of the blood was estimated by means of his carbon monoxid method. When 

 an individual is allowed to breathe a mixture of oxygen and carbon monoxid in 

 which the latter is present in small but known percentage, the hemoglobin 

 combines partly with the oxygen and partly with the carbon monoxid in defi- 

 nite proportions. After equilibrium has been established to this mixture the 

 percentage saturation of the hemoglobin with carbon monoxid may be deter- 

 mined upon a sample of blood, and from this figure the percentage saturation 

 with oxygen may be estimated. Experiments of this kind made at high alti- 

 tudes (Pike's Peak, 14,100 feet) indicated that the oxygen pressure in the blood 

 was 35 nuns, greater than in the alveolar air. As collateral evidence he cites the 

 case of the swim-bladder in deep-sea fishes. The gas in this bladder is known 

 to be nearly pure oxygen, and it may exist under a pressure of 100 atmospheres, 

 although in the blood of the fishes the oxygen-pressure cannot exceed to jV 

 of an atmosphere. 



