498 Historical 



Chemical explanations. The idea that under a greater baro- 

 metric pressure the blood, as it passes through the lungs, is laden 

 with a greater proportion of oxygen, is a very natural idea, which 

 was accepted by all the authors, up to the time of and including 

 Brize-Fradin (page 444). It found an obvious confirmation in the 

 observation made by Pol and Watelle, Frangois, Foley, and all the 

 physicians who attended caisson workers, that the blood drawn 

 from the veins during the compression, or even some time after 

 the decompression, is red and arterial in color. The apparently 

 contradictory experiments of M. Fernet (page 249) did not make 

 much impression on the authors in the face of this very obvious 

 fact. Only M. Bucquoy (page 459) tried to discuss them; in his 

 opinion, it is only the dissolved oxygen whose proportion increases, 

 because M. Fernet has proved that the blood corpuscles do not 

 absorb a greater quantity of oxygen in compressed air than in free 

 air. The other authors merely state that the blood is richer in 

 oxygen, and draw from that all the conclusions which they think 

 inspired by logic, a .guide which one must always distrust in these 

 complex matters. 



For M. Foley, for example, "the hyperarterialization" of the 

 blood cannot be doubted, and it results in "an enormous consump- 

 tion of the different tissues, because of the excess of oxygen which 

 penetrates them." But the existence of this increase in the intra- 

 organic combustions would have to be proved. 



But the experiments of MM. Regnault and Reiset, showing 

 that animals which breathe in a medium with very high oxygen 

 content do not absorb more of this gas and do not form more car- 

 bonic acid there than in ordinary air, showed that the idea of an 

 increased chemical activity was not very probable. Pravaz, the 

 only one who with Panum (page 480) seems to have understood 

 the import of the objection, makes a rather unsatisfactory reply to 

 it (page 448) in such a way as to compromise his reputation as a 

 physicist a little. But he did have two of his plipils, Hervier and 

 Saint-Lager, perform experiments tending to settle the difficulty 

 directly. 



We know what complicated conclusions (page 449) these ex- 

 perimenters reached when they tried to determine the modifica- 

 tions which a stay in compressed air makes in the excretion of 

 carbonic acid and consequently in the consumption of oxygen. I 

 shall not try to discuss them, because such researches are of value 

 only because of the method employed; I have already stated that 

 this method was extremely faulty. In so delicate a matter, in 



