422 Z)r. Wells’s Observations and 'Experiments 
for the rays which are reflected from the first surface are without 
colour, and, by hypothesis, none can be reflected from its inter- 
nal parts. In the next place, let there be dispersed through this 
black mass a small number of particles, differing from it in re- 
flective power, and it will immediately appear slightly coloured; 
for some of the rays, which have penetrated its surface, will 
be reflected by those particles, and will come to the eye ob- 
scurely tinged with the colour, which is exhibited by a thin 
layer of blood, when placed between us and the light. Increase 
now by degrees the number of those particles, and in the same 
proportion as they are multiplied, must the colour of the mass 
become both stronger and brighter. 
Having thus shewn that a black mass may become highly 
coloured, merely by a considerable reflexion of light from its 
internal parts ; if I should now be able to prove, that both 
common air and the neutral salts increase the reflexion of light 
from the internal parts of blood, at the same time that they 
brighten it, great progress would certainly be made in esta- 
blishing the opinion, that the change of its appearance, which 
is occasioned by them, depends upon that circumstance alone. 
But the following observations seem to place this point beyond 
doubt. 
I compared several pieces of crassamentum of blood, which 
had been reddened by means of common air and the neutral 
salts, with other pieces of the same crassamentum, which were 
still black, or nearly so ; upon which I found, that the red- 
dened pieces manifestly reflected more light than the black. 
One proof of this was, that the minute parts of the former 
could be much more distinctly seen than those of the latter. 
IJvJow this increased reflection of light, in the reddened pieces. 
