on the Colour of Blood. 42 9 
exposed to the atmosphere under mucilage of gum arabic, does 
not become florid. 
It has been said,* that neither serum, nor solutions of the 
neutral salts, dissolve the red matter of blood. But this in- 
duction has been made from too small a number of experi- 
ments. For saturate solutions of all the neutral salts, which 
I have tried, will extract, though slowly, red tinctures from 
blood, some of which are very deep; and neither they, nor 
serum, added in any proportion to a solution of the red matter 
in water, alter its colour or transparency, except by diluting 
it. The following experiments, however, will place this point 
in a clearer light. 
I added a drachm of distilled water to an ounce of serum, 
and poured the mixture upon a small piece of crassamentum. 
Upon an equal piece' of crassamentum I poured a drachm of 
water, and after some time added an ounce of serum. Each 
parcel, therefore, contained the same quantity of crassamen- 
tum, serum, and water ; but the crassamentum upon which the 
mixture of serum and water had been poured, communicated 
no tinge to it ; while the other piece, to which water had been 
first applied, and afterwards serum, gave a deep colour to the 
fluid above it. I made similar experiments with crassamentum, 
water, and a dilute solution of a neutral salt, which were at- 
tended with the same results. 
Since then neither serum, nor a dilute solution of a neutral 
salt, will extract colour from blood, though they are both ca- 
pable of dissolving the red matter, when separated by water 
from the other parts of the mass, it follows, in my opinion, 
that what are called the red globules consist of two parts, one 
* Fordyce’s Elements of the Practice of Physic, p. 14. 
3 K 2 
