CHEMISTRY OF THE LIVER. 323 



is taken up on a rod and allowed to cool, the reaction has gone far 

 enough. Decant from this mass and evaporate the liquid resulting until 

 a crystallization of salt forms. Filter and evaporate to a small volume. 

 If salt separates filter again and pour the liquid finally into a large excess 

 of alcohol. This causes the taurin to separate ; wash the crude substance 

 with strong alcohol, and recrystallize from hot water. In a successful 

 separation large plates or prisms of taurin are obtained. The substance 

 may be recognized by several tests. On heating it chars and gives off 

 an odor of sulphurous acid. When fused with sodium carbonate the sul- 

 phur is converted into sulphide, from which hydrogen sulphide may be 

 separated and identified by the usual tests. 



THE BILE PIGMENTS. 



The two substances biliverdin and bilirubin are related to 

 hematin from hemoglobin, as pointed out above, and as may 

 be illustrated b these formulas : 



Hematin 



Hematoporphyrin 

 Bilirubin 

 Biliverdin 



The two bile pigments are formed in the liver and normally, 

 apparently, only in the liver, but by what kind of reaction is 

 not clearly known. Hematoporphyrin may be produced from 

 hematin and it is isomeric with bilirubin, though not identical. 

 The relation of bilirubin to blood is perhaps best shown by 

 this observation: in old blood extravasations the blood color 

 appears to be gradually decomposed and in its place the new 

 coloring matter is found, which was called hematoidin by its 

 discoverer. Later studies showed the identity with bilirubin. 



Bilirubin is practically insoluble in water, but it seems to 

 act as an acid, the alkali salts of which are soluble. In this 

 form it exists in bile. The solution is reddish yellow and in 

 the air or by treatment with oxidizing agents it takes up oxy- 

 gen and becomes biliverdin, which gives a green solution. 

 The bile always contains the two pigments, from which the 

 greenish yellow color follows. The amount of the two sub- 

 stances in the bile is normally very small, but as the reactions 

 are sharp recognition is easy. The total weight of the two 



