226 Historical 



attributes them to the lack of the support of the air upon the 

 blood vessels: 



The pressure of the atmosphere (he says) upon the human body 

 is equal to a weight of 30,000 to 36,000 pounds; it keeps the mechanical 

 arrangements of the organism in their normal state, and gives con- 

 siderable help to the circulation, restraining the flow of the blood 

 towards the surface . . . Symptoms caused by congestions in various 

 organs have sometimes been noted on lofty mountains, where the air 

 is greatly rarefied. (P. 325.) 



One of the great difficulties always encountered by authors is 

 the lack of proportion between the severity of the symptoms and 

 the elevation which the travellers have reached, and that not only 

 in different hemispheres, but in the same country, on the same 

 chain of mountains. 



That is why the German Poeppig, 4 "' who gave such a complete 

 description of the mountain sickness of the Andes, cannot make 

 up his mind that the cause of it is the decrease of the atmospheric 

 pressure: 



The idea that the Puna, the Veta, does not depend upon the rare- 

 faction of the air, but upon a change in its composition, finds support 

 in the observation that the illness is not always in proportion to the 

 elevation of a place above sea level. The cabin of Casacaucha is 

 nearly at the same level as Cerro de Pasco, the pass of Viuda is a 

 thousand feet higher, and I have never felt the slightest distress there. 

 (Vol. II, p. 84.) 



M. Boussingault 46 also was struck by these variations; but bolder 

 than Poeppig, he seeks an explanation of them: 



In all the excursions I undertook in the Cordilleras, I always felt, 

 at an equal height, an infinitely more painful sensation when I was 

 climbing a slope covered with snow than when I was mounting over 

 bare rock; we suffered much more in scaling Cotopaxi than in ascend- 

 ing Chimborazo. On Cotopaxi we were constantly mounting over 

 snow. 



The Indians of Antisana assured us also that they felt stifled 

 (ahogo) when they walked for a long time over a snowy plain; and I 

 confess that after considering carefully the discomforts to which de 

 Saussure and his guides were exposed when they bivouacked on Mont 

 Blanc, at the moderate height of 3888 meters, I am disposed to attribute 

 them at least in part to the still unknown effect of snow. In fact, their 

 bivouac did not even reach the elevation of the cities of Calamarca 

 and Potosi. 



In the lofty mountains of Peru, in the Andes of Quito, the travel- 

 lers and the mules which carry them sometimes suddenly experience 

 a very great difficulty in breathing; we are told that animals have 

 been seen to fall in a state very like asphyxia. This phenomenon is 



