382 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



The acids formed as cleavage products from human bile are cholalic, 

 choleic, and fellic acids. 



Cholalic acid and its allies, on boiling with acids, on heating in the 

 dry state, or by putrefaction, lose water, and become converted into 

 anhydrides, or, as they are called, dyslysins. The dyslysin corresponding 

 to cholalic acid has the formula C 24 H3 G 3 ; it is found in faeces ; is a white 

 amorphous substance, insoluble in water and alcohol, soluble in ether 

 and melting at 140 C. Another compound, choloidinic acid, is formed, 

 as an intermediate stage, of the formula C 24 H 38 4 . On boiling with 

 alkalies, dyslysin takes up water, and is reconverted into cholalic acid. 



The bile pigments and their derivatives. The variations in the 

 colour of bile early attracted attention, and Gmelin, 1 in 1826, first 

 obtained proof of a relationship between these colours, and described 

 the test which still bears his name. *He was aware that the play of 

 colours was due to a process of oxidation, and made an experiment to 

 illustrate this by acidifying bile with hydrochloric acid, and enclosing 

 it in a tube from which the air was shut oft" by a mercury trap. Under 

 these circumstances no change in colour took place; but on exposing 

 the acidified bile to the air, a green colour slowly developed. He also 

 accurately described the play of colours obtained on oxidising with 

 nitric acid. 



Berzelius 2 precipitated biliverdin from ox bile with barium chloride, 

 purified it to some extent, and described its properties, but he fell into 

 the error of supposing that it was identical with chlorophyll. 3 



Heintz, 4 preventing oxidation by exclusion of air, extracted from 

 gallstones a brown amorphous pigment, which he named biliphain. 

 He analysed it, and converted it by dissolving in sodium carbonate, and 

 leading oxygen through the solution into a green pigment, biliverdin. 

 His biliphain corresponded to the bilirubin of the present day, and his 

 experiment shows well the connection between the two pigments. 



Valentiner, 5 in 1859, was the first to obtain bilirubin in a crystalline 

 form, by dissolving in chloroform, from which, on evaporation of the 

 solvent, it crystallises in microscopic crystals. From this discovery 

 onwards, research 011 the bile pigments took a more exact form, as 

 methods for the isolation of the pigments were discovered and perfected. 6 



Although a considerable number of more or less well-characterised 

 bile pigments have been described, only two are found under normal 

 conditions in the bile, these are bilirubin and biliverdin ; the others are 

 obtained by artificial means from these, are found under pathological 

 conditions only in the body, or are formed after death. The colour of 

 the bile is a compound of the colour of these two pigments, and varies 

 with the varying ratio of their amounts through all shades between 



1 Tiedemann and Gmelin, " Verdauung nach Versuchen," 1826. 



2 "Chemie," S. 281. 



3 The spectra of phylloporphyrin and hsematoporphyrin and their derivatives are almost 

 identical, and in other respects the substances closely resemble each other, so that there is 

 undoubtedly a relationship between them (Sclmnck and Marchlawski, Proc. Roy. Soc. 

 London, Jan. 1896). Now, phylloporphyrin is a derivative of chlorophyll, and hfemato- 

 porphyrin is isomeric with bilirubin, so that there may be some remote connection between 

 biliverdin and chlorophyll. 



4 Jahresb. u. d. Fortschr. d. ges. Med., Erlangen, 1851, Bd. ii. S. 59; Ann. d. Phys. 

 u. Chem., Leipzig, 1851, Bd. Ixxxiv. S. 106. 



5 Jahresb. ii. d. Fortschr. d. ges. Med., Erlangen, 1859, Bd. ii. S. 87. 



6 Briicke, Untersuch. z. Naturl. d. Mensch. u. d. Thiere, Bd. vi. S. 173 ; Stadeler, 

 Vrtljschr. d. naturf. Gesellsch. in Zurich, 1863, Bd. viii. S. 1 ; Ann. d. Chem., Leipzig 

 1864. Bd. cxxxii. S. 323. 



