UROERYTHRIN. 623 



The change from bilirubin to hydrobilirubin may be thus ex- 

 pressed 



C 3 ,H 36 N 4 O tt + H 2 + H 2 = C 32 H 40 N 4 7 



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 blood pigment in the 

 organs, independently of hepatic agency. 



Of the precise nature of the ckromogen 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-band 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 and 

 difficult of investigation. 



It was first dealt with as far back as 1800, by Louis Proust, 

 under the name of acide rosacique. Its present name was assigned 

 to it by F. Simon in 1850 the term "purpurin," earlier proposed by 

 Golding 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 Eiva, 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 off 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 (Riva). 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 be 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, Jo-urn. 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. 



