246 Historical 



1. All pressures exerted by the ambient atmosphere upon the 

 human body naturally oppose each other and balance each other 

 perfectly. 



2. The force exerted by the weight of the atmosphere is, more- 

 over, counterbalanced by the incompressibility of the liquids with 

 which all our organs are imbued, and by the tension of the gases and 

 vapors in the splanchnic cavities and interstices. Thus the skin is 

 placed between two forces which strive in opposite directions and 

 cause an equilibrium. 



Then he asks himself: 



Whence comes the difference (a difference, the nature of which 

 he unfortunately does not explain) observed between the corpse and 

 the living body in the reaction of the two to outer pressure? Should 

 we attribute it entirely to the difference in temperatures? But the 

 temperature of the human body is not high enough to give a tension 

 of more than 3 or 4 centimeters of mercury to the vapors of the 

 liquids which it contains. Should it be attributed to the gases dis- 

 solved in these liquids? But the experiments of Magnus prove that 

 if their quantity, merely for some of them, reaches proportions suffi- 

 cient to carry the tension of the liquids containing them to a figure 

 which equals or surpasses the atmospheric pressure, their action and 

 their reaction, with reference to the atmosphere, would be purely 

 physical. Now Magnus has shown, on the contrary, that the gases 

 dissolved in the blood are retained there by quite other forces than 

 simple pressure. For it is not enough to raise the temperature or to 

 lower the outer tension, even to just a few centimeters, to expel the 

 gases dissolved in the liquids of the body; it requires the presence of 

 other gases for which the blood has a greater affinity than for the 

 normal gases which it contains. Where then shall we find the inner 

 force which balances the ambient pressure? In the study of the laws 

 of circulation and pressure in the great vascular systems. 



The author then shows that, in the living animal, because of 

 the circulation of the blood, the tissues are always in a state of 

 tension which he estimates at from 8 to 15 millimeters of mercury. 

 Since this tension is constant, the result is, he says: 



That the organic system of the living being is never endangered 

 by even a great variation, if it is gradual, of the outer pressure and 

 that the circulation would continue as it was before the variation. 

 And this explains the data collected by M. Poiseuille and by M. Tingu, 

 in regard to the continuation of the vital functions, in spite of a 

 considerable increase of the ambient pressure. 



The dangerous power of the gases of the blood, freed by the 

 decrease of pressure, a hypothesis which Robert Boyle was the 

 first to express and which M. Giraud-Teulon strongly opposed, as 

 we have just seen, found an able defender in Felix Hoppe. 82 The 

 work of this chemist is of a purely experimental type; it was 



