150 



35. But there is art amazing difference between the 

 fixed and the common air, with regard to their effects 

 upon animal bodies. The fixed air, even when set free, 

 and in a state of perfect elasticity, whether it be during 

 the first stage of fermentation by fire, by effervescence, 

 or by putrefaction ; if it be received into the lungs of 

 any animal, causes instant death. But the same air, 

 when received into the stomach, whether thrown off* by 

 effervescent mixtures in medicine, or extricated from the 

 food by natural fermentation ; in the first instance often 

 operates like a charm, in restraining vomitings $ and in 

 the second is absolutely needful, for the support of life 

 and health. 



With regard to the common air, on the contrary, no 

 animal can live long without taking large quantities of 

 it into the lungs. Yet if a small portion of it be forced 

 into the blood-vessels of any animal, death presently 

 ensues. 



So that these two species of air have quite different 

 provinces, with respect to animal life. The first, com- 

 mon air, must mix wholly with the blood. The second 

 only communicates some subtle matter to it : probably 

 electric fire, which we know is connected with every par- 

 ticle of common air. 



