41 8 Dr. Wells's Observations and Experiments 
of blood into thin slices, and exposed them to common air. 
When they became florid, I put them into a phial containing 
distilled water. I then took as much of the same crassamen- 
tum, which was still black, and infused it in an equal quantity 
of distilled water, contained in a phial similar in size and shape 
to the former. The two solutions which were thus obtained, 
one from florid blood, the other from black blood, were, not- 
withstanding, of precisely the same colour. These experiments 
were frequently repeated, and were attended with the same 
results, as often as I used certain precautions, which shall be 
mentioned hereafter, as the reasons for them will then be more 
readily understood than they can be at present. 
Assuming therefore as proved, that neither common air, nor 
the neutral salts (for all those I have tried are similar to nitre 
m this respect) change the colour of the red matter of blood ; 
1 shall now attempt to explain the manner in which those sub- 
stances give, notwithstanding, to black blood a florid appear- 
ance ; premising, however, some observations upon the colours 
of bodies in general. 
It was the opinion of Kepler,* that light is reflected with- 
out colour from the surfaces of bodies ; which he says is easily 
proved, by exposing to the sun’s light a number of cups filled 
with transparent liquors of different colours, and receiving the 
reflexions from them upon a white ground in a dark place. 
Zucchius, who was younger than Kepler, but for some time his 
cotemporary, taught more explicitly , -f that the colours of bodies 
depend, not upon the light which is reflected from their anterior 
surfaces, but upon that portion of it which is received into their 
* Paralipomena in Vitellionem, p. 23 et 436. 
f Optica Philosopbia, Pars I. p. 278 et seq. 
