Decreased Pressure 953 



only at a certain level, and that where the oxygen lack of the blood 

 has reached a sufficient degree, and we shall make this expression 

 exact in a moment. If aeronauts are not attacked until long after 

 mountain climbers, it is not because their reserve of ternary mate- 

 rials is intact, for they have only to make some efforts and they too 

 become sick, it is because their muscles in repose do not demand 

 of the impoverished arterial blood a quantity of oxygen which it 

 would be unable to furnish them. Does that mean that the dif- 

 ferent causes of fatigue play no part in the conditions of the ap- 

 pearance of mountain sickness? I have already replied to that 

 question; but it is doubtful that it is a matter of the using up of 

 the ternary materials, since a sleepless night, an indigestion, some 

 indisposition or other have the same unpleasant consequences. A 

 tired man presents the best conditions for the development of 

 mountain sickness; but it does not recognize fatigue as its cause, 

 since if fatigue operates alone, mountain sickness never appears. 



M. Forel, whose works were discussed in our first part, wholly 

 adopted my ideas in his third Memoire. 6 I reproduce here the 

 interesting account of an excursion made by this physicist into a 

 grotto in which the air was very poor in oxygen, an account which 

 we must compare with that of M. F. Leblanc and also, because of a 

 remarkable coincidence of symptoms, with my experiment CCLIV. 



On June 23, 1864, I made an exploratory tour of the Grotte-des- 

 Fees of St-Maurice, a very profound cavern, which, among other 

 peculiarities, has an atmosphere very poor in oxygen; here is the result 

 of one of the analyses which Professor Bischoff made on air collected 

 1000 meters from the entrance of the cavern. 



Nitrogen 82.66 



Oxygen 15.33 7 



Carbonic acid 1.99 



If I calculate the oxygen tension in this air, I see that it is 14.7%, 

 the normal tension on the seashore being 20.9. This number corre- 

 sponds to the air tension at an altitude of more than 2000 meters. 



After a stay of several hours in this cavern, studying my physio- 

 logical state, I observed: acceleration of pulse, acceleration of respira- 

 tory rate, and mental disturbances which I described then in the 

 following terms: When I wanted to count my pulse, I was obliged 

 to try seven times; I was often mistaken, I skipped numbers, I counted 

 twice in succession the same group of ten, or I counted a group of ten 

 beginning at the end. 



The almost complete similarity of symptoms of mental disturb- 

 ances observed by M. Bert and myself, at such a great interval and 

 under such different outer conditions, seemed to me worthy of being 

 noted. (P. 88.) 



