234 Historical 



accustomed to the air of the mountains, and who endure great 

 fatigue. 



We can hardly doubt that, whatever the form under which it 

 presents itself, its appearance is due to the decrease in the weight of 

 the air, whose effect everyone feels in very lofty places. (P. 69.) 



Hill does not hesitate to declare that animals can become almost 

 completely acclimated to lofty places: 



The effects of the rarefied air are not limited to man; they exert 

 equal, if not greater, action upon the other animals of creation. The 

 horses and the mules of the plains cannot cover the same distance in 

 a given time on the mountains as on the plain; they are not capable 

 of carrying as heavy burdens on the Sierra as in the climates in which 

 they are accustomed to living. 



However, these animals, when they have been taken to consider- 

 able heights and are well cared for, become acclimated, in most cases, 

 after a few months, and they become fit to do almost the same work 

 as animals born in these lofty regions. (P. 69.) 



The physiologists continued, nevertheless, but without great 

 success, to seek for the causes of these symptoms noted, explained, 

 or denied by travellers. One of them, M. Maissiat, 64 whom his pro- 

 found knowledge of physics has often inspired to better result, tak- 

 ing up an explanation which we have already seen mentioned by 

 Clissold, in 1822, gives an important part to the abdominal gases, 

 expanded by the decrease in pressure: 



Their pressure stimulates the diaphragm and regulates the fre- 

 quency of its contractions; therefore, the circulation is linked with 

 the production of the intestinal gases. (P. 253.) 



If the pressure enveloping the animal diminishes, there will be 

 acceleration of the circulation and respiration and congestion of the 

 skin, and if the pressure continues to diminish, delirium or even death 

 may result; since the pressure of the abdominal 'gases increases in 

 its effects proportional to the decrease in the outer pressure, these 

 gases expand and distend the entire abdomen even to the point of 

 rupture, if the drop in external pressure is very rapid .... 



The accelerated circulation and respiration tend to speed up the 

 abdominal action, and thus to restore equilibrium and quiet regu- 

 larity. (P. 254.) 



The German physician, Flechner,* 55 reports an opinion quite con- 

 trary to that of Boussingault and von Humboldt upon the compo- 

 sition of the air of lofty places; he opposes it, it is true, and pre- 

 fers the last idea suggested by de Saussure. I quote from the 

 review in Schmidt's Jahrbuch: 



According to the general opinion, the air in the mountains is 

 richer in oxygen, from which inflammatory diseases result .... 



