Refpiration , and the life of the Blood. 245 
been. The ferum of the blood, therefore, appears to be 
as wonderfully adapted to anfwer its purpofe, of a vehicle 
for the red globules, as the red globules themfelves : for 
the flighted: covering of water, or faliva , effectually pre- 
vents the blood from acquiring its florid colour; and Mr. 
cigna found that this was the cafe when it was covered 
with oil. 
That it is really the air, aching through the ferum, and 
not the ferum itfelf, that gives the florid colour to the blood, 
is clearly afcertained by the following experiment. I 
took two equal portions of black blood, and put them 
into equal cups, containing equal quantities of ferum, 
which covered them to the depth of half an inch. One 
of thefe cups Handing in the open air, and the other being- 
placed under an exliaufled receiver, the former prefently 
acquired a florid colour, while the other continued twelve 
hours as black as at firft. Being taken out of the receiver, 
it flood all night in the open air without becoming red, 
and continued black ever after, even when the ferum was 
poured off. 
I alfo more completely fatisfied myfelf of the influence 
of the air upon the blood, through a body of ferum, by 
the reverfe of this experiment. For I found that red 
blood became black through the depth of two- inches of 
ferum, when the veffel containing it was expofed ta 
phlogiflicated air;, fo that the red globules of the blood 
both receive, and part with phlogifton by means of the 
air, notwithftandmg the interpofition of a large body of 
the fluid in which they naturally float. 
Except 
