390 PHYSIOLOGY CHAP. 



he determined the tension of the gases in the circulating arterial 

 blood, and that of the expired air at the tracheal bifurcation. 

 He repeatedly found that the partial pressure of the carbonic acid' 

 of the blood was less, and that of the oxygen greater, than the 

 respective partial pressures of the two gases in expired air. 



In some of Bohr's experiments, for instance, the partial pressure 

 of the O 2 and C0 2 varies as follows : 



2 of arterial blood = 100-144 mm. Hg. 



Og of expired air, at tracheal bifurcation . . = 95-130 



C0 2 of arterial blood = 17-30 



C0 2 of expired air, at tracheal bifurcation . = 35- 41 



Against these results of Bohr, the objection that he did not allow 

 sufficient time for equilibrium of tension to be established between 

 the gases of the arterial blood and the artificial air contained in 

 the aerotonometer, has no weight, because in this air, before the 

 entrance of the arterial blood, the partial pressure of the 2 was 

 less, and that of the CO 2 was greater, than after the experiment. 

 On the basis of these facts, which are opposed to the theory of 

 diffusion as the sole determinant of pulmonary gas exchanges, 

 Bohr puts forward the hypothesis that the walls of the pulmonary 

 alveoli function as a secreting gland, and that the cells that line 

 them are capable of actively absorbing oxygen and exhaling 

 carbonic acid, even against the laws of the diffusion of gases. 



Fredericq in his latest work does not accept Bohr's conclusions. 

 He invariably finds the tension of oxygen in the arterial blood 

 to be less, and that of carbonic acid greater, than the respective 

 tensions of the two gases in alveolar air. But this (as Tigerstedt 

 has pointed out) does not contradict the phenomena observed 

 by Bohr. One single fact, determined under valid experimental 

 conditions to be irreconcilable with the exclusive theory of 

 diffusion, gives legitimate reason to suspect that other forces 

 intervene in the production of gas exchanges, and are capable of 

 accelerating the effects of diffusion, and even of acting in 

 opposition to its laws. The study of this interesting question 

 deserves to be pursued without prejudice, the more so as Bohr 

 has discovered another fact that appears to be of the utmost 

 importance. After collecting and analysing the gases contained in 

 the swim-bladder of certain fishes caught at a great depth, he 

 found them to contain as much as 80 per cent oxygen. On 

 puncturing and emptying the swim-bladder, he found that it filled 

 anew with oxygen, but only on condition that the nerve plexuses 

 leading to it were spared. Once this fact is admitted, the 

 legitimate conclusion must be that the cells lining the swim- 

 bladder (which may be regarded as a modified lung) function as 

 glandular elements secreting oxygen under the influence of the 

 nervous system, and contrary to the laws of diffusion ; just as the 



