APP.] CHEMICAL BASIS Of 1 THE ANIMAL BODY. 765 



of the placenta. It is not found, or occurs in traces only, in gall- 

 stones. 



Preparation. An impure product is obtained by precipitating 

 ordinary herbivorous bile with baric chloride, washing the precipitate 

 with water and alcohol and decomposing it with hydrochloric acid. 

 The biliverdin thus obtained is washed with aether and dissolved in 

 alcohol. From its solution in the latter itis obtained as an amorphous 

 green powder by slow evaporation. Pure biliverdin is best prepared by 

 the slow oxidation in the air of bilirubin dissolved in dilute caustic 

 soda. 



It does not crystallise, and is insoluble in aether or chloroform ; readily 

 soluble in alcohol. When oxidised it gives the same play of colours as 

 does bilirubin, with the formation of the same final and intermediate 

 products. 



Neither this body nor bilirubin gives any characteristic absorption 

 bands. 



There seems now no reason for doubting that the bile pigments are 

 derived ultimately from the colouring matter of the blood. (See p. 30.) 

 Yirchow has described 1 the gradual changes in old blood-clots, 

 as of cerebral haemorrhage, which lead to the presence of the so-called 

 haematoidin crystals. Though these have not been obtained in sufficient 

 quantities to enable their composition to be finally fixed by a chemical 

 analysis 2 , still the identity of their crystalline form with that of bilirubin 

 and the fact that they both give the same play of colours when oxidised, 

 as in Gmelin's test, justify the assumption that haematoidin and bilirubin 

 are identical 3 . Moreover the balance of experimental evidence distinctly 

 supports the view that a liberation from the corpuscles of the colouring 

 matter of the blood in the blood-vessels by an injection of chloroform, 

 water &c., leads generally to the appearance of bile-pigments in the urine 4 . 

 The occurrence of bilirubin crystals in the urine has frequently been ob- 

 served after the operation of transfusion of blood in man. The chemical 

 possibility of the conversion of haemoglobin into biliverdin is readily 

 seen by a comparison of the formulae of haematin (see p. 341) and 

 bilirubin. The former has, according to Hoppe-Seyler 5 , the composition 

 indicated by the formula 2 (C M H^ N 4 Fe 5 ) while that of bilirubin is 

 C 16 H 18 N 2 O 3 . Although the conversion has not as yet been directly 

 effected the following facts are significant. If bilirubin is treated with 

 sodium amalgam the substance known as hyclrobilirubin (see below) is 



1 Arch. f. path. Anat. Bd. i., S. 383. 



2 Robin, Ann. d. Chem. u. Pharm. Bd. cxvi. S. 89. 



3 But see also Preyer, Die Blutkrystalle, 1871, S. 187. 



Tarchanofif, Pfliiger's Arch. Bd. ix. (1874), S. 53. See also Bd. x. (1875) 



6 Physiologisclie Chemie, 1879, S. 395. 



