544 



THE RESPIRATORY EXCHANGE 



a temperature of 39. In different experiments it is arranged that 

 the pressures of the gases in the tube shall in one case be greater, 

 in another case less than the anticipated pressures of the corre- 

 sponding gases in the blood. The gases in the tubes after the 

 blood has passed through them are analysed, and from the altera- 

 tion in the proportions the partial pressures of the gases in the 

 blood are calculated. 



With this instrument Pniiger's pupils, Strassburg, Wolffberg, 

 and Nussbaum, made a series of experiments upon dogs, and found 

 the pressure of carbon dioxide in the arterial blood to be 2*2 to 

 3-8 per cent., with a mean of 2-8 per cent, of an atmosphere, and 

 that of the venous blood from the right side of the heart 3- 81 to 

 5-4 per cent. Simultaneous determinations of the pressures of the 

 gases in the air removed by the lung-catheter were not made in 

 each case, but those results, in which that condition was fulfilled, 

 have been tabulated by Bohr, and are here reproduced. 



The general result ist hat the pressure of carbon dioxide in 

 the venous blood is about the same as that in the sample of 

 air obtained with the lung-catheter, and this could be explained 

 by diffusion alone. In two cases, however, the pressure in the 

 alveolar air was 1 per cent, higher than in the venous blood. The 

 experiments upon the pressure of oxygen were unsatisfactory. 

 Herter, who also made determinations with the aerotonometer, 

 found low values for the pressure of oxygen in arterial blood, the 

 highest value being 10*44 per cent, of an atmosphere. 



One of the chief criticisms of these results is directed against 

 the method of obtaining a sample of the alveolar air from the 

 portion of the lung blocked up by the balloon of the lung- catheter. 



