398 PHYSIOLOGY CIIAI-. 



Urobilin was separated from the urine of fever-patients by 

 Jaffe (186S), but in normal urine he found a chromogen which is 

 readily converted into urobiliu, not only by the action of acids, but 

 also by mere exposure of the urine to air and light. On spectro- 

 scopic examination the acid solutions of urobiliu show an absorp- 

 tion band which corresponds with the transition from 'green to 

 blue, more precisely between & and F. (See Vol. I. Fig. 35, p. 110.) 



Maly's hydroibilirubin gives a very similar spectrum, as also 

 the stercobilin found by Vanlair and Masius in the faeces. It is 

 therefore not improbable that urobilin is identical with hydro- 

 bilirubin and stercobilin. But they differ in other respects, and 

 the question has not yet been decided. 



The amount of urobilin in normal urine after the whole of the 

 urobilinogen has been converted into pigment varies, according to 

 Saillet, from 30 to 130 mgrms. per diem. According to Arcangeli 

 and Cavazza, under normal conditions, 65 nigrnis. urobilin are ob- 

 tained on an average from man, and 60 mgrms. from woman. 

 It increases considerably in fevers, in many infectious diseases, in 

 all the anaemias accompanied by exaggerated haernoly tic processes, 

 in many hepatic diseases, etc. 



Urobilinogeu is undoubtedly derived from blood pigment and 

 the bile pigments, particularly from bilirubin. It is certain that 

 the chief part of the urobilin and urobilinogen of the urine 

 originates in the intestine from the bile pigments, in consequence 

 of the fermentative processes due to intestinal microbes. The 

 following facts can be adduced in support of this theory : 



(a) Urobilinuria occurs when the putrefactive processes of the 

 intestine are exaggerated (Harley). 



(&) Urobilin is absent in the urine of the newborn before any 

 bacteria penetrate the intestine (Fr. Miiller), while stercobilin is 

 at the same time absent from the faeces (Eiva). 



(c) Urobilin is absent in adults after complete occlusion of the 

 bile passages, and makes its appearance again when the flow of 

 bile to the intestine recommences (Beck, Eiva, and Zoja). 



(d) On estimating the urobilin and urobilinogen of the urine 

 and the faeces, there is in every case a certain proportionality 

 (Eiva). 



The formation of urobilinogen from bilirubin in the intestine 

 does not take place by simple hydrolysis, as Maly believed from 

 his work on hydrobilirubin, but by a more profound metamorphosis 

 of the bilirubin molecule. This loses half its nitrogen, as shown 

 by Garrod and Hopkins from quantitative elementary analyses of 

 the elements of these substances, as obtained by various means 

 and from various sources. 



The most favourable conditions for the formation of urobilinogen 

 from bilirubin occur in the normal course of the functions of the 

 intestine. Nearly the whole of the urobilinogen formed in the 



