23& Dr. Priestley’s Obfervations on 
(liquid have imagined, they would produce the fame 
effeCt on the air in which they were performed. 
That refpiration, however, is, in reality, a true phlogiftic 
procefs, cannot, I think, admit of a doubt, after its being 
found, that the air which has lerved for this purpofe is 
left in precilely the fame fate as that which has been ex- 
poled to any other phlogiftic procefs. And ftnee all the 
blood in the body paffes through the lungs, and, accord- 
ing to Mr. hewson’s obfervations and others, the re- 
markable change between the colour of the venal and 
arterial blood takes place there, it can hardly he doubted, 
that it is by means of the blood that the air becomes 
phlogifticated in palling through the lungs; and there- 
fore, that one great ufe of the blood mult be to difeharge 
the phlogifton with which the animal fyftem abounds, 
imbibing it in the courfe of its circulation, and imparting 
it to the air, with which it is nearly brought into contact, 
in the lungs ; the air thus acting as the great menftruum 
for this purpofe. 
Though I had no doubt concerning this conclulion 
from my former experiments, I thought fo great a pro- 
blem deferved as much illuftration as could be given to it ; 
and therefore I was willing to try, whether the blood was 
of fuch a nature, as to retain any of this power of affect- 
ing air when congealed, and out of the body, that it has 
when it is fluid, and in the body; and the experiments 
have fully anfwered my expectations. 
Having taken the blood of a fheep, and let it ftand till 
ft was coagulated, and the ferum was feparated from it 
(after which the furface, being expoled to the common 
air, 
i 
