Refpiration , and the U/e of the Blood. 247 
of a fheep, and alfo took fome that came firft after killing 
it, as the butchers ufually do, by dividing the carotid ar- 
tery; but though I diffolved the black part of the for- 
mer, and the red part of the latter, in equal quantities of 
the fame fpirit of nitre, I found no fenfible difference in 
the air that they yielded. The air that I got from them 
when dried, and made into a pafte with fpirit of nitre, 
was likewife equally indiflinguifhable. The quantity of 
air from this procefs was very great, and was produced 
irregularly, as I have obferved it to have been when pro- 
duced by a folution in fpirit of nitre without drying. 
Obfervations on Air , vol. II. p. 155. Half of this pro- 
duce was fixed air, and the red: phlogiflicated, except that 
a candle burned in it with a lambent blue flame. It is 
evident, however, from this experiment, that even the 
mofl florid blood contains a confiderable quantity of 
phlogifton ; for, otherwife, this air would have been de- 
phlogiflicated. 
I would conclude this paper with obferving, that I 
have found a very great difference in the conftitution of 
blood with refpedt to its property of being affected by the 
influence of the air ; fome becoming very foon of a light 
florid colour, and the Jlratum of this colour foon grow- 
ing very thick; whereas, in other cafes, the colour of 
the blood, in the mofl favourable circumflances, has con- 
tinued much darker, and the lighter colour has never 
penetrated very far. 
As the principal ufe of the blood feems to be its power 
of receiving and difcharging phlogifton, and the degree 
in 
