324 VETERINARY PHYSIOLOGY 



taurin, H2N.CH2CH0.SO2OH, which is amino-acetic acid 

 linked to sulphuric acid. This is joined to cholalic acid. 

 In man there is very little taurocholic acid. 



Since both are amino-acids, they must be derived from 

 proteins. That they are formed in the liver and not merely 

 excreted by it, is shown by the fact that, while they accumu- 

 late in the blood if the bile duct is ligatured, they do not 

 appear if the liver is excluded from the circulation. The bile 

 salts manifest the following actions : — 



(i.) They are solvents of lipoids, and they activate 

 the lipase of the pancreatic secretion. For this reason 

 (a) they assist in the digestion and absorption of fats. 

 When bile is excluded from the intestines no less than 30 

 per cent, of the fats of the footl may escape absorption and 

 appear in the fasces. When this is the case, as in jaundice 

 in man from obstruction of the bile duct, the fasces have a 

 characteristic white or grey appearance from the abundance 

 of fat. (b) They keep cholesterol in solution, (c) They 

 act as powerful hsemolytic agents dissolving the lipoid 

 capsules of the erythrocytes and allowing the escape of 

 hasmosrlobin. 



(ii.) While the salts have no action on proteins, free 

 taurocholic acid precipitates native proteins and acid meta- 

 proteins. 



(iii.) They lower the surface tension of solutions, and 

 in this way they may bring the fat and other substances 

 into more intimate contact with the mucous membrane, 



(2) Bile Pigments. — These amount to only about 0'2 per 

 cent, of the bile. In human bile, the chief pigment is an 

 orange-brown iron-free substance, bilirubin, CggHgeN^Og, 

 while in the bile of herbivora, biliverdin, a green pigment, 

 somewhat more oxidised than bilirubin, C32H3gN408, is more 

 abundant. By further oxidation with nitrous acid, other 

 pigments — blue, red, and yellow — are produced, and this is 

 used as a test for the presence of bile pigments (Gmelin's test) 

 {Gheinical Physiology). 



The pigments are iron-free, and they are closely allied to 

 hsematoporphyrin and hasmatoidin (see p. 491). The}- are 

 derived from hsemo^lobin bv the splitting of the hasmatin 



