Refplration, and the Ufe of the Blood. 2 3 () 
air is well known to affiime a florid red colour, while the 
infide is ot a much darker red, bordering upon black) I 
introduced peces of the craffamentum, contained in nets 
o open gauze, or ot wire, fometimes through water, and 
iometimes through quickfilver, into different kinds of air, 
nnd always found that the blacked parts affirmed a floiid 
led colour in common air, and more efpeciallv in de- 
p llogilhcated air, which is purer and more fit for refpi- 
ration than common air (and accordingly the blood al- 
ways acquired a more florid colour, and the change was 
produced in lefs time in this than in common air) whereas 
t ie brighteft red blood became prefently black in any 
ind of air that was unfit for refpiration, as in fixed air, 
inflammable air, nitrous air, or phlogitticated air; and 
alter becoming black in the laft of thele kinds of air it 
i egained its red colour upon being again expofed to com- 
mon air, or dephlogifticated air; the fame pieces becom- 
mg alternately black and red, by being transferred from 
phlogifhcated to dephlogifticated air; and vice verfd. 
In thefe experiments the blood muft have parted with 
its phlogifton to the common air, or dephlogifticated air, 
and have imbibed it, and have become faturated with it’ 
when expofed to phlogifticated, nitrous, inflammable, or 
xed air. The only difficulty is with refpedt to the fixed 
air; for all the other kinds certainly contain phlogifton. 
But, as I have obferved in the account of my experi- 
ments on vitriolic acid air, phlogifton feems to be necel- 
lary to the conftitution of every kind of air; and befides 
t ie blacknefs of the blood may arife from other caufes 
than 
