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the red particles, or globules as they are called, which,, 
fay they, being in greater proportion at the bottom 
of the Craffamentum, makes it appear black; but, 
if inverted, the globules then fettle from the furface 
which is now uppermoft, and that becomes redder. But 
this I think is not probable ; for the lymph in the 
crajfamentum is fo firmly coagulated, as to make it 
too denfe, to allow of bodies even heavier than 
the red particles to gravitate through it ; for example 
gold. That air has the power of changing the co- 
lour of the blood, has been long known ; and the fol- 
lowing experiment Ihews it very fatisfattorily, and 
hardly leaves room to refer the appearance to another 
caufe. 
Experiment III. 
Having laid bare the jugular vein of a living rab- 
bit, I tied it up in three places ; then opening it be- 
tween two of the ligatures, I let out the blood, and 
filled this part of the vein with air. After letting it 
reft a little till the air fhould become warm, 1 took 
oft the ligature, which feparated the air from the 
blood, and then gently mixed them, and I obferved 
that the venous blood afi'umed a more florid rednefs, 
where in contact with the air-bubbles, whiift at 
ether parts it remained of its natural colour. 
There is a difference between the arterial and ve- 
nous blood in colour; the former is of a florid red 
like the furface of the Crajj amentum, the latter is 
dark or blackifh like the bottom of the craffamen- 
tum. This change in its colour is produced on the 
blood as it paffes through the lungs, as we fee by 
opening 
