240 Historical 



As to the differences presented by different individuals with 

 reference to the altitude at which mountain sickness attacks them, 

 Pravaz finds reason for that in the inequality of "the resistance of 

 their tissues and in the vital contractility of their lungs". The 

 sudden appearance of symptoms, a suddenness which our 

 author exaggerates, is due to the fact that "in an almost indi- 

 visible moment, the atmospheric pressure becomes less than the 

 reaction of the lung, and ceases to be able to struggle successfully 

 against it. . . . The decrease of the quantity of oxygen contained 

 in the air breathed would not be great enough to explain this fact, 

 for this decrease . . . could bring on dyspnea only gradually". 

 (P. 76.) 



Be that as it may in regard to this last restriction, up to that 

 time the alternative explanation given by de Saussure had been 

 accepted without dispute, an explanation which tends to attribute 

 the discomforts of decompression chiefly to the insufficient quan- 

 tity of oxygen which the respiratory acts bring into the lungs. But 

 in 1851, Pay erne, 74 an engineer who gave much attention to diving- 

 bells, raised an objection to this hypothesis, the worth of which 

 we shall discuss later: 



Upon the highest summits ever ascended, the pressure is equal at 

 least to 32 cm. of mercury. The air there contains still 125 gm. of 

 oxygen per cubic meter, or 100 gm. per 800 liters which a man- 

 breathes per hour. Now experiments, the accuracy of which no one 

 could question, have recently shown that a man while resting con- 

 verts only 50 gm. of oxygen into carbonic acid. Assuming that while 

 at work he would convert 5 and even 10 gm. more, he will be far 

 from lacking it in a place where the barometer stands at 32 centi- 

 meters .... 



The weariness and the panting in lofty places therefore do not 

 seem to me to come from an insufficiency of oxygen, but from the 

 rupture of the equilibrium between the tension of the fluids contained 

 in our organs and that of the ambient air, no matter in which direc- 

 tion the rupture operates. 



The authors who followed Payerne seemed not to have known 

 of his objections. Marchal de Calvi, 75 among others, reproduces 

 purely and simply the former explanation; this is shown by the 

 extract from his work, published by the Proceedings; this extract 

 we quote in full: 



The author thinks that he can conclude from the experiments 

 reported in this Note that the variations in the atmospheric pressure 

 are far from exerting the influence attributed to them. According to 

 him, the mistake comes from the fact that in most cases which have 

 been considered, when there is a decrease in pressure on the surface 



