CHEMICAL BASIS OF THE ANIMAL BODY. 249 



which are still less conclusive. For the present the evidence of close 

 relationship if not of absolute identity suffices fully as a basis for our 

 belief in the genetic relationship of the bile and urinary pigments 

 and of the ultimate derivation of these from the colouring-matter of 

 the blood. 



During his earlier researches on the pigments of blood Hoppe-Seyler 

 described a product resulting from the reduction of hsematin in acid 

 solution by the action of zinc and hydrochloric acid, characterised by 

 one absorption band between b and F and, as he then said, two other 

 bands 1 . After the appearance of Maly's work he was led to suspect 

 that the substance he had previously described was in reality identical 

 with hydrobilirubin and therefore with urobilin, a conclusion which he 

 verified by a careful repetition of his earlier experiments 2 . 



More recently Nencki and Sieber have prepared a similar pigment by the action 

 of hydrochloric acid and zinc on their hsematoporphyrin, to which latter substance, 

 as was stated above, they assigned a formula identical with that of bilirubin. They 

 state however that the pigment (urobilin) is not quite identical as obtained on the 

 one hand by the action of nascent hydrogen on bilirubin and on the other hand on 

 their haematoporphyrm 3 . - 



Assuming then the identity of these substances we have in Hoppe- 

 Seyler's work the best and most direct chemical evidence of the 

 relationship between the colouring-matters of the blood and bile. For 

 if one and the same substance, viz. urobilin, can be prepared by the 

 same means, namely reduction (hydrogenation) from both hsematin 

 (hemoglobin) and bilirubin, these two substances must be themselves 

 closely related. It has not however as yet been found possible to 

 produce a bile-pigment directly from haemoglobin or hsematin by any 

 artificial process outside the animal body. The derivation of the 

 urinary pigments (urobilin) from those of bile presents no difficulty 

 when it is remembered that a not inconsiderable quantity of hydrogen 

 is present in the gases of the intestine ( 282) which may be accounted 

 for by (butyric) fermentative processes (p. 105), and that this hydrogen 

 might in its nascent state readily produce the simple change which 

 is known to occur when bilirubin is converted into hydrobilirubin or 

 urobilin. And here it is interesting to note that hydrobilirubin is 

 readily absorbed and excreted in the urine either when placed in the 

 alimentary canal or injected subcutaneously. 



The question of pigmentary relationships to which reference has 

 just been made suggests the present as a convenient place to enter 



1 Med.-chem. Untersuck. Hft. 4, 1871, S. 536. 



2 Ber. d. d. chem. GeselL Bd. vn. (1874), S. 1065. 



3 Monatsh. f. Chem. Bd. ix. (1888), S. 115 ; Arch.f. exp. Path. u. Pharmakol. Bd. 

 xxiv. (1888), S. 430. 



