196 TEXT-BOOK OF PHYSIOLOGY 



Sodium Glycocholate and Taurocholate. Of the various ingredients 

 of the bile none are more important than these two salts, usually known as 

 the bile salts. The sodium glycocholate is found most abundantly in the 

 bile of herbivora, the sodium taurocholate in the bile of the carnivora. These 

 salts are compounds of sodium and glycocholic and taurocholic acids. 

 When separated from the sodium, the acids will crystallize in the form of 

 fine acicular needles. Under the influence of hydrolizing agents, such as 

 dilute acids and alkalies, both acids will undergo cleavage into their re- 

 spective components e.g., glycocoll and cholic acid, taurine and cholic acid. 

 Glycocoll and taurine are crystallizable nitrogenized compounds known 

 chemically as amido-acetic and amido-isethionic acids respectively. 



From the results of the hydrolysis of the bile acids it may be inferred that 

 their formation in the liver cell is the result of an opposite process, viz. : a 

 synthesis of glycocoll and taurin with cholic acid. Glycocoll is an amino- 

 acid and there is much evidence that taurin is a derivative of cystin, another 

 amino-acid, both found in the small intestine. The origin of cholic acid is, 

 however, not so clear. The absorption of the foregoing compounds from 

 the intestine and their transmission to the liver cells by the portal vein fur- 

 nishes them with the necessary materials for the formation of the bile acids. 

 During the period the bile remains in the biliary passages, the biliary salts 

 hold cholesterin in solution. 



There is also good evidence for the view, that after their discharge into 

 the intestine, the bile salts are absorbed, with the exception of a portion de- 

 stroyed by bacteria, and carried by the portal vein to the liver and again 

 excreted. By this circulation from liver to intestine and from intestine to 

 the liver, the work of the liver cells in the synthesis or secretion of bile acids, 

 is supposed to be reduced to a minimum. It is also probable that a portion 

 of the acids enters the general circulation and influences favorably the gen- 

 eral nutrition. It is stated by some investigators that the activities of the 

 liver cells are decidedly increased by the circulation of the bile salts and that 

 they are to be regarded as the natural stimuli to the secretion. 



The presence of the bile salts can be demon- 

 strated by the employment of Pettenkofer's test 

 or reaction. It was shown by this investigator 

 that if to a solution of bile salts a small quantity 

 of a 10 per cent, solution of cane-sugar be added 

 and subsequently a small quantity of strong sul- 

 phuric acid, a brilliant red color appears which 

 soon passes into a rich purple. To secure the 

 best results in the performance of this test care 

 Stirling.) should be exercised to keep the temperature below 



7oC.; the characteristic colors appear to be due 



to the action of the sulphuric acid on the cane-sugar by which a sub- 

 stance, furfurol, is produced, which in turn reacts with the cholic acid. 

 This test can be applied to bile directly; thus if to bile in a test-tube cane- 

 sugar be added and the mixture thoroughly shaken, a portion of the bile 

 becomes quite frothy. If now sulphuric acid be carefully added, the red 

 and purple colors present themselves at once in the white froth an indica- 

 tion that the bile salts are distributed through it. 



Cholesterol. Cholesterol can be obtained directly from bile or better 

 from white gall-stones by the employment of chemic methods described in 



