206 Historical 



As on the first time, all these operations were carried out within two 

 minutes after the sparrow had been inserted. This animal showed the 

 same symptoms as the first. It lived 70 minutes; at its death, the 

 mercury had risen 7 lines above the point at which it stood at the 

 beginning. 



Finally I placed a third sparrow in the bottle, without having 

 rarified the air (the height of the mercury was then 27 inches, 6 lines). 

 The symptoms were the same with the exception of the convulsions. 

 The animal lived three hours and a half. At the time of its death, 

 the mercury had risen in the siphon about 1 inch and IV2 lines. 



In these experiments, the quantities of enclosed air were to each 

 other as the numbers 128, 169, 330, and consequently almost as 3, 4, 8. 

 The duration of life of the sparrows was as the numbers 35, 70, 210, 

 and almost as 1, 2, 6; whence it follows first that in airs of different 

 density, it does not correspond to the quantity of air, but increases in 

 greater proportion than the quantity of air when its density is greater, 

 and consequently, that the same quantity of air supports the life of 

 the animals longer when it is condensed than when it is rarefied. 

 (P. 165.) 



From these experiments Cigna draws the following conclusion: 



A rarefied air is not harmful to the life of animals from its rarity, 

 but because it is altered sooner than when it is denser; for in such an 

 air, the animals breathe at first without difficulty; their respiration 

 becomes labored only by degrees, and in proportion to the' capacity 

 of the receiver; in a word, everything goes on just as in an air with 

 its natural density. If the air were harmful on account of its rarity, it 

 would be equally harmful no matter what the capacity of the receiver 

 might be. (P. 166.) 



And to prove it, he performs a double experiment, in which two 

 sparrows were subjected to the same very low pressure (from 9 1 /? 

 to 714 inches), one in a closed bottle, the other in a receiver in 

 which he renewed the air frequently. The first died, whereas the 

 second was "full of health" after more than a half-hour: 



I conclude from this experiment (he says) that an air, extremely 

 rarefied under the pneumatic receiver, is capable of maintaining respi- 

 ration and life, provided it is renewed, and that is why animals 

 endure the condensation of enclosed air much better than an equal 

 rarefaction; that is also why a flame burns and animals live on the 

 highest mountains, although the air there is extremely rarefied, 

 whereas they soon die under a receiver in which the air has been 

 rarefied to the same degree. (P. 167.) 



But I call particular attention to the remarkable explanation 

 which Cigna gives for the harmlessness (which he certainly exag- 

 gerates greatly) of air which is rarefied and renewed: 



It is obvious that the air needs only to be dense enough to expand 

 the lungs by its pressure; now to expand the lungs, this pressure 



