456 Historical 



We should note that Hoppe never made direct experiments on 

 this point, and that he reasons only by analogy. 



As to the effect of the compression itself, he says merely: 



The increase of the air pressure must increase the capacity of 

 the blood to absorb gases; the blood will then contain more oxygen, 

 from which will result a greater production of heat and a decrease 

 of the quantity of air breathed in a given time. The observation of 

 Pravaz of a lessened quantity of carbonic acid excreted in compressed 

 air is explained by the small volume of air used in his experiments. 

 (P. 71.) 



Dr. Frangois, 18 after the account which we have quoted of the 

 symptoms appearing in the workmen at the bridge of Kehl, in- 

 quires into their cause. He first rejects the opinion of Guerard 

 about rheumatism, and one of the reasons he gives is that "the 

 muscular pains disappear spontaneously if the workmen go back 

 into the compressed air." The explanation which he gives of these 

 pains is very strange: 



They are (he says) the evident result of introduction into the 

 tissues of compressed air, forced in by the blowing machines, and this 

 air blends with the cellular tissue in its innermost parts, as, for ex- 

 example, mercury blends with hog's lard after a careful trituration, so 

 that not a molecule of metal is perceptible to the naked eye. 



This air, thus accumulated beyond measure in our tissues, must 

 seek to establish an equilibrium with the ambient atmosphere at the 

 time of leaving the compressed air, and the more hasty is this depar- 

 ture from the air chamber, the less gradual it is and the less prolonged 

 is the elimination, the more pronounced the pathological effects must 

 be, for the reason mentioned above. 



He explicitly rejects, as Pol and Watelle had done, any com- 

 parison between superoxygenated air and compressed air: 



We cannot agree that these pains are produced by the presence 

 of an air with a higher oxygen content, as has been suggested; in fact, 

 every atmosphere of compressed air contains, with all its other ele- 

 ments, only the same proportion of oxygen that it contains on the out- 

 side: it is not an excess of oxygen that is forced into the caissons, 

 but rather an excess of atmospheric air. 



We are therefore inclined to admit that the muscular pains are 

 the result of a constant effect exerted upon the tissues by an excess 

 of atmospheric air, an irritation sometimes rising to the most acute 

 pain, when this air seeks too suddenly to find an equilibrium with a 

 less dense medium. (P. 309.) 



So much for the muscular pains. As to symptoms affecting the 

 respiration, these are pulmonary congestions, M. Frangois says: 



