Theories and Experiments 449 



pressure of 0.76 meters; this difference between the conditions of 

 absorption makes us anticipate a corresponding difference between 

 the results given by an inspiration of pure oxygen and one of merely 

 compressed air. (P. 23.) 



Experimentation, according to him, confirms this idea of the 

 theory. This experiment is the one of Hervier and St.-Lager 

 (page 446) , whose conclusions Pravaz accepts, and whose apparent 

 contradictions he explains as follows: 



The endosmosis of oxygen, which is the principal duty of respira- 

 tion, is aided by all circumstances which increase the solubility of this 

 gas in the blood; now the increase of atmospheric pressure is evidently 

 included in these circumstances, according to the experiment reported 

 by M. Biot; so in compressed air there must be a supersaturation of 

 the venous blood by oxygen, but this phenomenon cannot manifest 

 itself immediately by a greater exhalation of carbonic acid, for the 

 exosmosis of this gas is kept down by the same mechanical force 

 which increases the absorption of oxygen. 



When the respiration is once more taking place in normal atmos- 

 phere, the superoxidation of the blood corpuscles which was produced 

 during the compressed air bath necessarily gives rise to symptoms of 

 vital exaltation and to the elimination in greater quantity of the 

 gaseous product of the combustion of carbon, which has become 

 more active because this gas is no longer subjected to the increased 

 pressure which restrained its expansibility .... 



Analogy leads us to think that the same thing is true of nitrogen 

 as of oxygen. Has its increased absorption some advantage for metab- 

 olism? I am inclined to think so, judging by the observations of 

 Regnault and Reiset upon the absorption of nitrogen from the air by 

 animals in a state of inanition ... so that this gas ... . would seem 

 to be intended .... to supply the place, in a certain degree, of 

 alimentation by the digestive organs. If one admitted this very plau- 

 sible hypothesis, he would have a new datum to explain the good 

 effects obtained by the use of the compressed air bath in cases where 

 there is weakness of the digestive functions through debility. (P. 28.) 



C. Compressed air aids the return of the venous blood to the 

 heart. 



Pravaz states first that compression decreases the number of 

 arterial pulsations: he has even seen it reduced 2/5, "especially 

 when a feverish state existed previously." Then he stresses the 

 fact that the suction "exerted by the right auricle and the thoracic 

 cavity" is one of the most active causes of the venous circulation, 

 and he adds: 



The capillary system, as a result of the increase of the barometric 

 pressure, must empty into the veins more easily, for not only has the 

 peripheral action of the force which compresses this network and the 

 veins into which it empties become more energetic, but also the 



