^42 A MANUAL OF VETERINARY PHYSIOLOGY 



animals. It is possible also that some of the pigment is re- 

 absorbed from the intestinal canal, carried to the liver, and again 

 eliminated. The value of this circulation of bile pigment is 

 unknown. 



The Bile Salts are two in number — glycocholate and tauro- 

 cholate of soda ; they are formed in the liver by the union of 

 cholalic acid with glycin or taurin, and exist in combination 

 with soda. These salts are found in varying proportions in 

 different animals ; thus, glycocholate of soda is largely found in 

 herbivora, taurocholate principally in carnivora, while in the pig 

 hyoglycocholic and hyotaurocholic acids are found. Both salts 

 are soluble in water, have a markedly alkaline reaction, rotate 

 the plane of polarised light to the right, and may be obtained 

 in a crystalline form as highly deliquescent acicular needles. 

 Glycocholic acid is the chief bile acid in herbivora ; it is produced 

 by the union of glycin with cholalic acid ; it is diminished by an 

 animal and increased by a vegetable diet. Taurocholic acid is 

 produced from taurin and cholalic acid, and exists principally 

 in carnivora, though small quantities may be found in the ox. 

 This acid differs from the first characteristically by containing 

 sulphur, by which it shows its proteid origin. Glycin or glyco- 

 coll also owes its origin to the proteids of the food, and if adminis- 

 tered it reappears externally as urea. It cannot be traced in the 

 free state in the body, but occurs in the urine combined with 

 benzoic acid, in the form of hippuric acid. Pettenkofer's test for 

 bile acids is performed as follows : A drop of the fluid is placed 

 on a white earthenware surface, and to it is added a drop of a 

 strong (10 to 20 per cent.) solution of cane sugar, and a similar 

 quantity of strong sulphuric acid ; a beautiful purple-red colour 

 forms. The colour is due to furfurol, and is produced by the 

 action of the acids on the sugar and the subsequent reaction with 

 cholalic acid. 



The origin of the bile acids is involved in obscurity ; taurin 

 may be formed from cystin, and this is capable of yielding taurin 

 on oxidation ; cystin is an end-product of protein disintegration ; 

 glycin may also be formed from protein. The precursors of 

 cholalic acid are unknown ; nor do we know why glycin should 

 predominate in some animals and taurin in others. It appears 

 clear that the bile salts are formed in the liver cells. In the 

 intestines a portion of the bile salts is reabsorbed, carried to the 

 liver, and again excreted ; or they may be split up in the intestines 

 into their constituents, the glycin and taurin being carried to 

 the liver to be reutilised, while the cholalic acid is excreted. 

 This economical measure, the second of its kind noted in connec- 

 tion with the liver, has a twofold advantage, for not only can the 

 glycin and taurin be used over and over again, but the bile 



