228 Dr. Priestley’s Obfervations on 
cerning the life of refpiration, from haller’s excellent 
Svflem of Pbyjiology , and fome others of the mold eminent 
writers upon that lubjedt. 
Hippocrates reckoned air among the aliments of the 
body. But it was more generally the opinion of the an- 
cients, that, there being a kind of Vital fire kept up in the 
heart, the heat of the blood was tempered in the lungs. 
galen alfo fuppofed, that, there was fomething equiva- 
lent to a fire conftantly kept up in the heart ; and that 
the chief ufe of the lungs was to carry off fuch vapours 
as were equivalent to fmoke thrown off from that fire. 
haller, vol. III. p. 354. cartesius maintained the 
fame vital fire in the heart, fuppofing that air was ne- 
ceffary for cooling and condenfing the blood. Ibid. p. 343. 
Of the more modern phyfiologifts, fome have thought 
that the air itfelf is taken into the lungs ; others, that it is 
only fomething extracted from the air, as the more fubtle 
parts of that fluid, an ether, or aerial nitre; while others 
fuppofe it to be the air itfelf, but diflolved in water, and 
therefore in an unelaft ic ft ate, ibid . p. 321. 
Mold of thofe who think that air is taken into the 
blood fuppofe it to be taken in by the lungs, ibid. p. 
330. Some fuppofe, that the effebt of the admiflion 
of this air into the blood is a fermentation, p. 332. 
Others fuppofe, that it a£ls by its fpring, preventing 
the too clofe contact of the globules, and thereby pre- 
ferving its fluidity, inteftine motion, and heat, ibid, ber- 
tier fuppofed, that the circulation of the blood was, m 
a great meafurc, owing to the admiflion of air into it. 
van iielmont afcribed the volatility of the fixed ele- 
ments 
