Refpi ration^ and the Ufe of the Blood. 235 
lamina^ which were black, they alio became fucce (lively 
red, till the whole mafs acquired that colour, Mifc. Tau- 
r in . vol. L p. 73. Alio, at the requeft of M. cigna, Fa- 
ther beccaria tried what would be the effect ot expofmg 
blood in vacuo ^ and he found, that in thole circum- 
ftances, it always continued black; but that, by ex poling 
it again to the air, it became red, p. 68 .* 
M .cigna concludes his firft differtation with obferving, 
that it is not eafy to fay ho it comes to pafs, that the lower 
part of a mafs of blood becomes black, whether by the air 
which it had imbibed efcaping from it, or by its depot it- 
ing fomething faline, neceffary to contribute to its red- 
nefs, or by the preflure of the atmofphere; but he in- 
clines to think, that air mixed with blood, and interpofed 
between the globules, preferves its rednefs : but that by 
concreting it" is expelled from it, or becomes fo fixed as 
to be incapable of making it red. This opinion, lie 
thinks, is rendered in fome meafure probable, by the in- 
creafed denfity of concreted blood, and by the emiflion 
of air from other fluids in a concrefcent ftate, p. 74. 
Notwithftanding what he had advanced in his firft 
Memoir, yet in the fecond, which was written feveral years 
after it, he doubts whether the change of colour in the 
blood takes place in the lungs; but if it does, he inclines 
to afcribe this effedt to the evaporation from the blood 
in the lungs : and though he always found, that the co- 
lour of the blood was changed by the contaft of air, yet 
when he confidered that evaporation muft, as he though 
neceflarily attend the contact of air, he imagined, that this 
H h 2 effeft 
