77 6 



CHEMISTR Y OF RESPIRATION. 



equal to that of the corresponding gas in the mixture. In the aero tonometer 

 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 



// Hi J 11U III -.-HI uncoagulable by the injection of 



sP It / 11 TflC peptone, in order that the experi- 



MU Hi f W 11 III llvt 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, 2*8 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 " haemat- 

 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 Nussbaum 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 CentralU. /. PhysioL, Leipzig u. Wien, 1893, S. 33 ; Fredericq et Nuel, ''Elements 

 de physiologic humaine," 3 e Edition, 1893, p. 156. 



2 Skandin. Arch. /. PhysioL, Leipzig, 1891. Bd. ii. S. 238. 



3 Bohr, loc. dt. ; Fredericq, CentralU. /.' PhysioL, Leipzig u. Wien, 1893, S. 33 ; 

 Haldane and Lorrain Smith. Journ. PhysioL, Cambridge and London, 1896, vol. 

 xx. p. 497. 



4 Arch. /. d. ges. PhysioL, Bonn, 1873, Bd. vii. S. 296. 



FIG. 73. Pfluger's aerotonometer. 



