ADDITIONS TO CHAP. IV. 
OF THE CHANGES INDUCED ON THE AIR BY THE 
RESPIRATION OP BIRDS, OF QUADRUPEDS, AND 
OF MAN. 
562. VV E before pointed out (79. et seq.) the 
general agency of water and heat in contributing to 
produce the phenomena of living action in the supe- 
rior animals; and from the writings of Boyle and 
others, we adduced facts to shew the constant neces- 
sity of fresh air to maintain the functions of life. 
This necessity Mayhow first proved to arise from the 
consumption of what he called the nitro-aerial or 
pure part of the air in respiration, which wholesome 
part was shewn by Dr Black to be converted into 
carbonic acid. By his discovery of oxygen gas, Dr 
Priestley was enabled to demonstrate the specific por- 
tion of the air which was thus changed * ; and M. 
* It should be mentioned, in justice to the celebrated Scheele, 
that he, likewise, discovered oxygen gas independently of Dr 
Priestley, as, in the following paragraph, the Doctor himsejf, with 
