494 Historical 



The rule to decompress slowly, aside from any theoretical idea, 

 has been accepted by all authors and proclaimed by the workmen 

 themselves, although in practice the intense cold which accom- 

 panies the decompression urges the latter to make haste. M. Foley 

 alone seems not to consider it important, and, on the contrary, ad- 

 vises rapid decompression (page 377). 



2. Theoretical Explanations. 



Here again we must separate the symptoms observed during the 

 stay in compressed air from the symptoms of decompression. 



A. Phenomena Due to Compression. 



Of course, there could be no question here of seeking elsewhere 

 than in the compressed air the cause of the symptoms reported 

 by experimenters or workmen; the strange hypotheses which we 

 have discussed in regard to mountain sickness could not be sug- 

 gested here. But this effect of compressed air was considered by 

 some from the physico-mechanical point of view, by others from 

 a purely chemical standpoint. I recall only for the record the 

 so-called explanation given by Brize-Fradin (page 444) , which ad- 

 vances the theory of "vital force," and then has recourse to it to 

 "change general laws" and settle things according to his desire. 



Physico-mechanical Explanations. Let us set aside, first as 

 really not worthy of discussion, the idea that air compressed to 

 several atmospheres would hinder the movements of locomotion, 

 and, second as too apparent, the effect of compressed air on the 

 tympanic membrane, of which we have already spoken. We are 

 first faced by the explanation which we have had to combat in 

 speaking of decompression, that is, the difference in the weight 

 sustained by the body. 



We have quoted the calculations which Guerard took pains to 

 make to show to what a crushing weight a man would be exposed 

 who is working under a pressure of several atmospheres. So the 

 workmen of the Kehl bridge would have had to sustain an addi- 

 tional weight of 54,000 kilograms. In fact, if, as we have already 

 shown (page 341), elementary physics did not pass sentence on 

 these ideas in the name of the incompressibility of liquids and 

 solids, these figures alone should have warned the authors of the 

 enormity of the error which they were committing. However, 

 almost all have accepted this explanation; M. Foley expresses it in 

 striking words: "As soon as one enters the caissons, one is flat- 

 tened" (page 464). 



