204 Proceedings of Royal Society of Edinburgh. [sess. ; 
A solution made on 1st of February, with thymol added, was a 
yellowish fluid, with some red precipitate, at the end of two years. 
A solution of CO-HbO, to which Am 2 S had been at once added, 
still showed after three years the two bands between D and E. 
A solution of CO-HbO to which nothing had been added, was 
at the end of two years a pale yellowish fluid. 
Some deductions can be drawn from these observations, extend- 
ing over three years, upon the permanence of Hb0 2 and its deriva- 
tives. They may be arranged in order of stability thus : — 
Very stable . — Acid Haematoporphyrin and its red ally in urine 
(a-Hsematoporphyrin) (9) ; Hb0 2 when in dilute antiseptic solution 
or when dried, Acid Haematin; then Alkali Haematin (whether 
chemically pure or made by putrefaction) ; Carbon-monoxide- 
Haemoglobin; Haemochromogen (of putrefaction). 
Moderately stable . — HbO ; Alkaline Met-Haemoglobin ; Neutral 
Met-Haemoglobin. 
Unstable . — Chemically Pure Haemochromogen. 
Very unstable. — Hb0 2 in presence of putrefaction. 
In connection with these pigments under observation for a very 
long time, it is noteworthy that in several instances, after reduction 
had done its work, there was formed a precipitate of something 
reddish, while something yellowish and transparent went into 
solution. This yellowish liquid was noticed in dilute solutions of 
Hb0 2 , HbO, CO-HbO, Haemochromogen, Acid Haematin, Neutral 
Met-Haemoglobin. This yellow pigment was not the yellow pig- 
ment of serum, because it was observed in dilute artificially-pro- 
duced solutions of Hb0 2 or its allies. 
I venture to think we have here a test-tube version of what 
occurs to blood-pigment in the body, chiefly in the liver, viz., 
first a reduction of the c effete ’ haemoglobin, followed by a de- 
composition of it into two portions, an iron-containing compound 
that can be demonstrated in the liver-cells, and iron-free substances 
— the parents of the biliary and urinary pigments, greenish or 
yellowish in colour. 
In a former paper (9) I tried to construct, based upon the ex- 
perimental work of others, a genetic tree of these pigments, but 
at that time had unfortunately not noticed a paper by Dr 
Eichholz (Cambridge) (11). Two of his results confirm the views 
