102 Mr. W. Brandf/s Chemical Researches on the Blood, 
gradually to subside, the coagulum having been removed: 
after twenty-four hours, the clear serum was decanted off, 
and the remainder, containing the colouring matter, after hav- 
ing been evaporated to dryness, was incinerated, and the ash 
examined as in former experiments. But the traces of iron 
were here as indistinct as in the other instances above men- 
tioned, although a considerable quantity of the colouring 
matter had been employed. 
The minutiae of analysis I have purposely excluded, as lead- 
ing into details which would exceed the proper limits of this 
paper, and unnecessary in the present investigation ; I shall 
now merely dwell on the principal results which have been 
obtained, and on the general conclusions which these afford. 
SECTION VI. 
Researches on the colouring Matter of the Blood. 
1. To procure this substance for experiments, I generally 
employed venous blood which had been stirred during its co- 
agulation ; the fibrina is thus removed, and the colouring 
matter diffused through the serum, from which it gradually 
subsides, being difficultly soluble in that fluid ; on decanting 
off the supernatant serum, the colouring matter remains in a 
very concentrated form. When other modes of procuring it 
were employed they will be particularly mentioned ; but as I 
have not found the serum which is retained interfere much 
with the effects of various agents upon the colouring principle, 
the method just noticed was commonly adopted. 
0. When the colouring matter thus collected is microsco- 
