CHEMICAL BASIS OF THE ANIMAL BODY. 245 



Preparation. An impure product may be obtained as follows from 

 herbivorous bile. After the removal of mucin (p. 77), barium chloride 

 is added; this precipitates the pigment as a compound with barium (1). 

 The precipitate is then collected on a filter, washed with water and 

 alcohol and decomposed with dilute hydrochloric acid ; this liberates 

 the biliverdin which is simultaneously precipitated as a flocculent mass 

 and is then washed with ether to remove all fat and dissolved in 

 alcohol. The alcoholic solution is finally filtered and by spontaneous 

 evaporation yields a dark-green glittering residue of impure biliverdin. 

 To obtain the pigment pure it must be prepared from bilirubin. The 

 conversion may be effected in several ways 1 , (i) Bilirubin is dissolved 

 in a dilute alkali and exposed for some time to the air in thin layers, 

 whereby it is slowly oxidised into biliverdin. When the conversion is 

 complete, the pigment is precipitated by the addition of hydrochloric 

 acid, thoroughly washed with water, dissolved in absolute alcohol and 

 precipitated by an excess of water or by spontaneous evaporation of 

 the alcoholic solution, (ii) By enclosing bilirubin solutions in tubes 

 with glacial acetic acid and heating to 100. (iii) By the action of 

 monochloracetic acid and gentle heating at intervals for one or two 

 days, (iv) Also by the action of caustic potash on tribromobilirubin 2 . 



Apart from its colour biliverdin differs most characteristically from 

 bilirubin in its solubilities. It is (like bilirubin) soluble in alkalis but 

 insoluble in water and ether, whereas (unlike bilirubin) it is insoluble 

 in either chloroform, carbon bisulphide or benzol, but readily soluble in 

 alcohol and in glacial acetic acid. It has further never been obtained 

 in a crystalline form, and like bilirubin it shows no absorption-bands 

 but a somewhat strong absorption of the violet end of the spectrum. 

 Treated with fuming (yellow) nitric acid it gives Gmelin's reaction, 

 starting now with a blue colour as a product of the first stage of its 

 oxidation. It also yields Huppert's reaction. (See above sub bili- 

 rubin.) 



Like bilirubin the quantitative determination of biliverdin is 

 dependent upon spectrophotometric methods 3 . 



The formula assigned above to biliverdin represents its formation 

 from bilirubin by simple oxidation 4 . This is undoubtedly correct as 

 against the older view of Staedeler that the change consists not only 

 in the assumption of oxygen but also of a molecule of water. 



Bilifuscin, bilihumin and biliprasin are the names given by Staedeler to 

 ill-defined and probably impure products obtained during his investigations on 



1 Maly, Sitzb. d. k. Akad. Wien, Bd. LXX. 3 Abth. 1874. Juli-Hft. 



2 Maly, Ibid. Bd. LXXII. 3 Abth. 1875. Oct.-Hft. 



3 See references sub bilirubin; 



4 Maly, loc. cit. Thudichum, Jl. Chem. Soc. July, 1876. 



