CA USES OF THE EXCHANGE OF GASES. 



777 



tidal air. Wolff berg l found that the expired air of a dog contained 2*8 

 volumes per cent, of carbon dioxide, or a tension of 21*3 mm. of mercury. 

 Strassburg 2 found a tension of 5*4 per cent, of an atmosphere for the 



FIG. 74. Frederick's 

 aerotonometer. 



FIG. 75. Bohr's lisemataerometer. 



carbon dioxide in the venous blood of the right side of the heart. This 

 value, higher than those obtained by Wolffberg and Nussbaum, could be 

 explained by the fact that the dog's lungs were not so well ventilated, 

 since tracheotomy had not been performed. In arterial blood Strass- 

 burg found the tension of carbon dioxide to be 2 '2 to 3*8 per cent, 

 of an atmosphere, and for the oxygen Herter 3 obtained a tension of 10 

 per cent, of an atmosphere. 



Very different results have been obtained by Bohr 4 in experiments 

 upon dogs. He obtained for the oxygen tension of arterial blood results 

 as high as 101 to 144 mm. of mercury, and in nearly every case the tension 

 was higher than the tension of oxygen in the air at the bifurcation of 

 the trachea, in one case by as much as 38 mm. As regards the tension of 

 carbon dioxide very discordant results were obtained. In eleven experi- 

 ments, in which the animal breathed pure air, the tension of the carbon 

 dioxide in the arterial blood varied between and 28 mm. of mercury; and 

 in five other experiments, when the air inspired contained carbon dioxide, 



1 Arch. f. d. ges. Pkysiol., Bonn, 1871, Bd. iv. S. 478. 

 -Ibid., 1872, Bd. vi. S. 77. 



3 Ztschr.f. physiol. Chem., Strassburg, 1879, Bd. iii. S. 98. 



4 Skandin. Arch. f. Physiol. , Leipzig, 1891, Bd. ii. S. 236. 



