77 6 
CHEMISTR Y OF RESPIRATION. 
equal to that of the corresponding gas in the mixture. In the aerotonometer 
the blood is made to pass in a thin layer through a glass tube or tubes, 
containing mixtures of gases of 
known quantity and tension, and 
it is arranged by practice that the 
tension of the gases in the tubes 
shall in the one case be greater, 
in the other case smaller, than the 
tensions of the corresponding gases 
in the blood. The gases in these 
tubes, after the blood has passed 
through them, are analysed, and 
from the alteration in the propor- 
tion in the two tubes it is possible 
to calculate the partial pressure 
of the gases in the blood. The 
aerotonometer is surrounded by a 
water-jacket with a temperature 
of 39°. 
Figure 74 shows the con- 
struction of a similar aerotono- 
meter, devised by Fredericq. 1 The 
blood of the animal is rendered 
uncoagulable by the injection of 
peptone, in order that the experi- 
ment may be continued for an 
hour or two. The blood flows 
directly from the carotid artery 
through the instrument, and re- 
turns to the jugular vein. 
The aerotonometer contains, for example, at the commencement of the 
experiment, oxygen 10 per cent,, carbon dioxide 5 per cent,, and nitrogen 85 
per cent, of an atmosphere. The blood is passed through for one hour, and at 
the end of that time the gases in the aerotonometer are analysed, and found to 
be 14 per cent oxygen, 2S carbon dioxide, and the remainder nitrogen. From 
these figures it is concluded that the tension of the oxygen in the blood was 
14 per cent, of an atmosphere, and that of the carbon dioxide 2*8 per cent, of 
an atmosphere. 
Bohr 2 had previously introduced a modified aerotonometer, the " hsemat- 
aerometer," through which a constant and rapid stream of blood could be 
maintained during each experiment (see Fig. 75). 
What, then, are the tensions of the gases of the blood '. The results 
obtained by different observers are very discordant, and have given rise to 
considerable discussion. 3 Xussbaum 4 determined simultaneously on a 
dog the tension of the carbon dioxide in the blood from the right side 
of "the heart and in the air of the alveoli ; he found for the former a 
pressure of 3-81 per cent, of an atmosphere, and for the latter 3 - 84 
per cent. The tension of the carbon dioxide in normal alveolar air 
would be lower, for it would be mixed to a certain extent with the 
1 GentraZU. f. Physiol., Leipzig u. AVien, 1893, S. 33 ; Fredericq et Nuel, "Elements 
de phvsiologie hnmaine." 3 e edition, 1893, p. 156. 
-SkaacHn. Arch. f. Physiol., Leipzig, 1891. Bd. ii. S. 238. 
3 Bohr, Joe. cit. ; Fredericq, Geviralbl. f. Physiol., Leipzig u. Wien, 1893, S. 33 ; 
Haldane and Lorrain Smith, Journ. Physiol., Cambridge and London, 1896, vol. 
xx. p. 497. 
i Arch, f. d. gcs. Physiol, Bonn, 1S73, Bd. vii. 8. 296. 
Fig. 73.— Pfluger's aerotonometer. 
