342 HUMAN PHYSIOLOGY 



the addition of water-free ether, which makes them separate 

 out as crystals. (Chemical Physiology, p. 21.) 



Glycocholic acid splits into glycin, amido-acetic acid 



H 



H \ 1 



>N C C O H 



i 



and a body of unknown constitution, cholalic acid, C^H^O^ 

 Taurocholic acid yields amido-ethane-sulphuric acid or 

 taurin. This is a molecule closely resembling amido-acetic 

 acid linked to sulphuric and cholalic acids. 



Since both acids contain nitrogen they must be derived 

 from proteids. That they are formed in the liver and not 

 merely excreted by it, is shown by the fact that, while 

 they accumulate in the blood if the bile-duct is ligatured, 

 they do not appear if the liver is excluded from the 

 circulation. 



Action of Bile Salts. 1. The bile salts are solvents of fats 

 and fatty acids, and they thus assist in the digestion and 

 absorption of fats. When bile is excluded from the intes- 

 tines no less than 30 per cent, of the fats of the food may 

 escape absorption and appear in the faeces. When this is 

 the case the feces have a characteristic white or grey appear- 

 ance from the abundance of fat. 



2. These salts keep cholesterin in solution. 



3. While the salts have no action on proteids, free tauro- 

 cholic acid precipitates native proteids and acid proteate. 

 In the human intestine this is an action of no importance. 



4. These salts are powerful ha^molytic agents, and rapidly 

 dissolve haemoglobin out of the erythrocytes. 



Bile Pigments. These amount to only about 0*2 per cent. 

 In human bile the chief pigment is an orange-brown sub- 

 stance, bilirubin, C 32 H 36 N 4 O 6 , while in the bile of herbivora, 

 biliverdin, a green pigment somewhat more oxidised than 

 bilirubin, C^H^N^Og, is more abundant. By further oxi- 

 dation with nitrous acid other pigments blue, red, and 

 yellow are produced, and this is used as a test for the pre- 

 sence of bile pigments (Gmelin's test). (Chemical Physiology, 

 p. 21.) 



