THE LIVER AND PANCREAS 24 i 



first a three-banded, and later, on standing, a four-banded 

 spectrum. These bands are due to cholohaematin, which is not 

 a bile pigment proper. The 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 the 

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

 which can be made to crystallise 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, forming 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 colour is observed ; this is 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 absent. 



Although bilirubin has not been obtained from haemoglobin, 

 there is no doubt that this is the source of the pigment, for if 

 haemoglobin be liberated in the blood and enters the plasma, 

 bile pigments appear in the urine ; further, haemoglobin may be 

 readily decomposed, yielding a protein and haematin ; and if 

 this haematin be deprived of iron, the residue thus obtained is 

 not very dissimilar in composition to bilirubin. We have pre- 

 viously mentioned (p. 13) that old blood-clots contain an iron- 

 free substance known as haematoidin, and this is practically 

 identical in composition with bilirubin. When red blood-cells 

 disintegrate in the ordinary course of their wear and tear, the 

 liberated haemoglobin is brought to the liver, and under the 

 influence of the liver cells converted into the iron-free substance 

 bilirubin or biliverdin. Part of the iron so liberated escapes 

 from the body through the bile, but the bulk of it is retained, and 

 again used in the formation of haemoglobin by the organs which 

 discharge this function. 



Though biliverdin is the colouring matter of the bile of herbi- 

 vora, yet the gall-stones found in the ox consist very largely of 

 bilirubin combined with chalk ; in the pig the same combination 

 is observed. Bilirubin is said by Hammarsten to be constantly 

 present in the serum from horse's blood, though not in that of 

 the ox, and Salkowski states that it is a normal constituent of 

 the urine of the dog during the summer. In the large intestines 

 both bilirubin and biliverdin undergo reduction, resulting in the 

 formation of stercobilin, the colouring matter of the faeces in some 



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