CHEMICAL BASIS OF THE ANIMAL BODY. 1303 



and colour it was further found that hsematoidin crystals readily 

 give the characteristic (Gmelin's) reaction for bilirubin by 

 treatment with nitric acid, and thus its identity with bilirubin 

 was at once asserted and supported by very convincing evidence. 

 The identity was however at one time disputed. There is how- 

 ever no doubt that haematoidin is really identical with bilirubin, 

 so that now the name is of interest rather from a historical 

 point of view, and physiologically as indicating the undoubted 

 genetic relationship of the pigments of bile to those of blood. 



BlLE-PlGMENTS AND THEIR DERIVATIVES. 



The bile is in all animals a characteristically highly coloured 

 secretion. The colour of the fresh bile is as a general rule 

 golden-red in man and carnivora, and more or less bright green 

 in herbivora. These colours are due to the presence of a pig- 

 ment known as bilirubin in the first case and biliverdin in the 

 second ; but since the latter pigment may be readily formed by 

 simple oxidation from the former, bile may frequently contain 

 both these colouring matters and hence possess a colour inter- 

 mediate to the above, though usually with a preponderance of 

 either the golden-red or green shade. In addition to these two 

 pigments others are occasionally present in bile, as evidenced 

 by the fact that while neither bilirubin nor biliverdin exhibits 

 any absorption bands when examined spectroscopically, fresh 

 bile of herbivora l frequently does shew bands, three or four in 

 number, due to substances of which but little is known beyond 

 these spectroscopic arjpearances. 



1. Bilirubin. 2 C 16 H 18 N 2 O 3 . 



It occurs chiefly and characteristically in the fresh bile of 

 man and carnivora, to which it imparts the well-known golden- 

 red colour. It frequently constitutes the larger part of some 

 kinds of gall-stones, more especially of the ox and pig, not as 

 free bilirubin but as a compound with chalk, and amounting to 

 some 40 p.c. of the concretions. It is also found in the urine 

 in icterus, also constantly in the serum from horses' blood, 

 though not from that of man or the ox, and frequently as crys- 

 tals under the name 'haematoidin' (see p. 1302) in old blood- 

 clots (extravasations) and fluids from ovarial and other cysts. 



1 Bile of carnivora does not usually shew bands until it has been treated 

 with an acid. 



2 This is the generally accepted formula. It is possible that the formula is 

 really twice the above, viz. CsaHse^Og as required to represent the formula of 

 a well-defined tribromo-substitution product, CsjHsaBrsN^V This doubling 

 of the formula is also necessary to express the derivation of hydrobilirubin 



from bilirubin. 



