The Liver and Pancreas. 161 



the principal constituent of certain gall-stones. It is kept 

 in solution in the bile by means of the bile salts. 



The Bile Pigments are two in number, bilirubin and bili- 

 verdin ; the latter is produced by oxidation from the former. 

 Bilirubin is the colouring matter of human bile and that of 

 carnivora, whilst biliverdin gives the colour to that of 

 herbivorous animals. 



Both pigments are insoluble in water, but soluble in 

 alkalies ; in the bile they are held in solution by the bile 

 acids and alkalies. Bilirubin may be obtained from gall- 

 stones of the ox in the form of an orange-coloured powder, 

 which can be made to crystallize in rhombic tablets and 

 prisms. If an alkaline solution of bilirubin be exposed to 

 the air it becomes biliverdin by oxidation, and this latter 

 pigment by appropriate treatment may be obtained as a 

 green powder. 



Both colouring matters of the bile behave like acids, form- 

 ing soluble compounds with metals of the potassium group, 

 insoluble ones with those of the calcium group (Bunge). 



On the addition of nitric acid (containing nitrous acid) to 

 the bile pigments, a play of colours is observed, known as 

 Gmelin's test. In the case of bilirubin the colours pass from 

 yellowish red to green, then to blue, violet, red, and yellow. 

 Each of these colours is indicative of a different degree of 

 oxidation of the original bilirubin. Biliverdin gives the 

 same play of colours excepting the initial yellowish red, 

 which is, of course, absent. 



Although bilirubin has not been obtained from haemo- 

 globin, there appears to be no reasonable doubt that this is 

 the source of the pigment, for haemoglobin may be readily 

 decomposed, yielding a proteid and htematin, and if this 

 hrematin be deprived of iron, the residue thus obtained is 

 not very dissimilar in composition to bilirubin. Old blood- 

 clots contain an iron free substance known as hamiatoidin, 

 which is identical in composition with bilirubin. The iron 

 which is found in the bile probably results partly from 

 the hcomoglobin after it has become converted into the iron 

 free substance bilirubin. 



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