208 Historical 



blood and the other humors". But Borelli did not continue long 

 in this opinion, and, absorbed exclusively by his theory of effort, 

 he narrowed the question greatly: 15 



I then perceived that this distress was not produced by the exces- 

 sive rarity of the air or by any corruption of its qualities, since, when 

 we were sitting down or were on horseback, naturally breathing the 

 same air, we felt no more oppression than on the seashore. I have 

 given a solution of this problem in my Meteorology 16 of the Fires of 

 Etna; but when I reflect upon it, I cannot remain in this opinion, and 

 I now come to a more probable explanation of it. (P. 242.) 



Borelli then reminds the reader that he has shown why a fa- 

 tiguing labor necessarily brings on panting. He will now show why 

 locomotion in rarefied air cannot take place without great fatigue, 

 whence comes the difficulty in breathing. (It is his proposition 

 CXXIII.) 



A labor can become fatiguing for two reasons: first, if the resist- 

 ance increases; second, if the strength lessens . . . 



The air contained in the chest, as I have said, helps the effort of 

 the muscles, compressing by its elasticity the air- and blood-vessels. 

 Therefore, when the air is very much rarefied, although it is com- 

 pressed by the thorax as the dense air was, it acts less upon the vessels, 

 and consequently aids the muscles less .... Therefore, in rarefied 

 air the same work will require greater effort, since the strength is 

 lessened, whence comes the lassitude, which was to be demonstrated. 

 (P. 243.) 



Bouguer 1T does not display any greater astuteness; the well- 

 known fact that under certain circumstances the symptoms attack 

 only those on foot and not horsemen makes him attribute them to 

 fatigue; for more serious cases, he resorts to the cold: 



What proves this irrefutably is that one is never exposed to this 

 illness when one is on horseback or when he has once reached the 

 summit, where the air, however, is even rarer. I do not deny that this 

 great rarity hastens lassitude and contributes toward increasing ex- 

 haustion, for respiration becomes extremely painful; however little one 

 exerts himself, he is all out of breath at the slightest movement; but 

 nothing of the sort takes place as long as one remains inactive. . . . 



We passed three weeks (August, 1737) on the summit of Pichincha; 

 the cold there was so keen that one of us began to feel some scorbutic 

 symptoms, and the Indians and the other servants whom we had en- 

 gaged in the country had violent colic: they passed blood, and some 

 were forced to descend; but when once we were camped on the edge 

 of the cliff, their illness was always the result of the severity of the 

 cold to which they were not accustomed, without the rarity of the air 

 seeming to be the cause of it, at least, not the immediate or near cause: 

 I investigated this the more carefully because I knew that most of the 



