33 2 Refpiration of Injefis, 6fr. [Book IX. 



oxygen' gas, and one or two parts in the hundred fixed 

 air. The azote is not proved to have any effect in 

 refpiration, and feems to be merely a diluent of the 

 oxygen gas, which is the principal agent. The fixed 

 air contained in the atmofphere is probably alfo com- 

 pletely inert with refpect to refpiration. Previous to 

 a more particular confideration of the nature of this 

 function, it may not, however, be improper to throw 

 together a few milcelianeous obfervations on that 

 fubject. 



Animals breathing air contaminated by refpiration, 

 not only fuffer for want of the pure part of that air, 

 which is deftroyed, but alfo from the fixed air which 

 is produced. Mr. Cavendifh afierts, that in certain 

 difeafes, and by certain peribns, the air is much fooner 

 rendered unrefpirable. According to the obfervations 

 of Dr. Prieftley, infects appeared to breathe fixed air, 

 or air otherwife contaminated, as readily as pure air. 

 Flies, however, and other winged infects, have the pro- 

 perty of deftroying the falubrity of air by their own 

 refpiration, as may be obferved by confining a few of 

 thofe animals in a phial. Thefe animals, indeed, 

 appear lefs of the amphibious kind, and much more 

 delicate, than when in the vermiform or maggot 

 ftate. 



Infects, and fome exfangnious animals, will exift 

 a confiderable time without any thing equivalent to 

 refpiration. The fame has been proved to be the cafe 

 with fifhes, though it is impoflible to define the limits 

 of their exiftence. 



A veiTel in which, when filled with common air, 

 a moufe could not live more than half an hour, was 

 filled by Dr. Prieftley with vital air ; a moufe then 

 lived in it for three hours, and being taken out alive, 



the 



