542 



THE RESPIRATORY EXCHANGE 



through, the elastic catheter. The results obtained :n this way 

 by WolfTberg and Nussbaum show that such samples of alveolar 

 air in dogs contain about 3*5 per ent. of carbon dioxide and 

 15-16 per cent, of oxygen at atmospheric pressure. 



Loewy and Schrotter have adapted this instrument for use 

 with the bronchoscope upon man. 



The samples of air obtained with the lung-catheter are not 

 true samples of alveolar air, but of the air in an occluded portion 

 of the lungs. If the process of exchange between the blood and 

 the air be a question of pressure only, the diffusion will proceed 

 until the pressures of the gases in the alveoli of the occluded portion 

 of the lung become equal to the mean pressures of the correspond- 

 ing gases in the blood which flows through the capillaries in the 

 walls of the alveoli. Thus there is considerable va 7 ue to be 

 attached to such samples, for, on the theory that the gaseous 

 exchange in the lungs is a process of diffusion, the pressure of 

 their constituent gases should be a measu r e of the respective gases 

 in the venous blood. It is uncertain, however, whether the gaseous 

 exchange is of such a simple nature ; according to Bohr, Haldane 

 and Lorrain Smith the pressure of oxygen in the arterial blood is 

 higher than the pressure of that gas in the alveolar air. 



The Causes of the Gaseous Exchange between the Blood and the 

 Alveolar Air. It is impossible to give a satisfactory account of 



