UR OER I 'TIIRI. X. 623 
The change from bilirubin fco hydrobilirubiii may be thus ex- 
pressed — 
C 11 .MK + iLii + iL^rji.^,!!. 
If urobilin differs from hydrobilirubin, the difference is possibly, 
as already stated, in the direction of increased reduction. 
The origin of urinary urobilin is probably threefold — from absorp- 
tion of the ready-formed pigment in the bowel; from direct production 
in the liver ; and, lastly, from reduction of the Wood pigment in the 
organs, independently of hepatic agency. 
Of the precise nature of the chromogen of urobilin we have no 
knowledge. It is precipitated intact when normal urine is saturated 
with ammonium sulphate in the absence of mineral acid. 1 It is possible 
that oxidation may decompose it, as some urines originally showing 
no absorption-hand will develop such on standing. This phenomenon 
might follow, however, from the decomposition during standing of 
some compound of the pigment with lime or other base. 
(c) Uroerythrin. — This pigment is best known as the colouring 
matter of pink urate deposits. It is a substance of the greatest interest, 
but one which has proved, from its marked instability, elusive ami 
difficult of investigation. 
It was first dealt with as far back as 1800, by Louis Proust, 
under the name of acidc rosacique. Its present name was assigned 
to it by F. Simon in 1850 — the term "purpurin," earlier proposed by 
Goldinw Bird, being; still sometimes used. Heller published an account 
of the pigment in 1854, and Macmunn first accurately described its 
spectrum in 1883. Very important contributions to our knowledge of 
uroerythrin have recently been made by Kiva, Zoja, and A. E. Garrod. 2 
The quantity of the pigment excreted is, under any circumstances, 
very small ; but its tinctorial power is extremely high, and when in 
solution it may materially contribute to the coloration of the urine. 
It is certainly to be looked upon as a pigment of normal urine, as 
urates coloured by it frequently separate from the excretion of persons 
in health. 
Separation. — A quantity of pink urate deposit is collected upon a filter, 
washed with ice-cold water, dried, and soaked in absolute alcohol. The 
alcohol, though a solvent for uroerythrin, does not extract it from the urates. 
The spirit is poured riff and the precipitate dissolved in warm water ; from the 
aqueous solution so obtained the pigment is easily and completely extracted by 
shaking with amylic alcohol (Kiva). Garrod has shown that if the pink urates 
are first dissolved in warm water, and are then reprecipitated by saturation 
with ammonium chloride, the pigment is carried down with them afresh, and 
in such a condition that it may now be extracted with alcohol. An alcoholic 
solution, if diluted with water, may be washed by shaking with neutral 
chloroform, which removes impurities but no uroerythrin. But if after this 
preliminary washing a fresh supply of chloroform is added, together with a 
single drop of acetic acid, on shaking, the pigment is now found to lie transferred 
completely to the chloroform as an effect of the acidification of the liquid. 
Properties. — The most striking properties of uroerythrin are — (1) Its 
remarkable affinity for uric acid compounds ; (2) the ease with which 
1 Eicholz, Journ. Physiol., Cambridge and London, vol. xiv. p. 326. 
- Journ. Physiol., Cambridge and London. 1895, vol. xvii. p. 439. Full references to 
the literature will here be found. 
