CA USES OF THE EXCHANGE OF GASES. 
Ill 
tidal air. Wolffberg 1 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 
=111 
Fig. 74. — Fredericq's 
aerotonometer. 
Bohr's hremataeroiueter. 
carbon dioxide in the venous blood of the right side of the heart. This 
value, higher than those obtained by Wolffberg and Xussbaum, 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 carl ion dioxide to be 2'2 to 3 - 8 per cent, 
of an atmosphere, and for the oxygen Herter :; 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 ah- 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. Physiol, Bonn, 1871, Bd. iv. S. 478. 
- Ibid., 1872, Bd. vi. S. 77. 
3 Ztschr. f. physiol. Chen., Strassburg, 1879, Bd. iii. S. 98. 
4 Skandin. Arch. f. Physiol., Leipzig, 1891, Bd. ii. S. 236. 
