THE DIGESTIVE SECRETIONS 947 



or with ammonium sulphid which, owing to their content in iron, 

 colors them dark brown. 



Special Constituents of Bile. The bile contains the sodium 

 salts of complex amino-acids, such as glycocholic, taurocholic, glyco- 

 choleic and taurocholeic. The relative proportion of these salts differs 

 in different animals, glycocholic acid being more abundant in the bile 

 of man and herbivora, and taurocholic acid in that of the carnivora. 

 They are formed as soon as the liver attains its full functional develop- 

 ment and do not arise elsewhere in the body. Their detection is 

 made possible by means of Pettenkofer's reaction, which consists in 

 adding a few drops of a 10 per cent, solution of cane-sugar and con- 

 centrated sulphuric acid to the suspected liquid. If the latter con- 

 tains bile salts, a violet ring develops at its point of contact with the 

 reagent. This coloration is due to the formation of an aldehyde-like 

 furfurol by the acid from the sugar, and the condensation of this prod- 

 uct with the bile salts. 



The bile salts may be prepared by mixing fresh bile with about 1 per cent, by 

 weight of animal charcoal. This liquid is evaporated to dryness on the water bath, 

 and the residue powdered and extracted with water and filtered. The filtrate is 

 acidified, but contains, in addition to the bile salts, also some cholesterol, mucin, 

 phosphatides and inorganic salts. Crystallized bile 1 is prepared in the same way, 

 excepting that the dried mixture of charcoal and bile is extracted with boiling ab- 

 solute alcohol. Since the bile salts are very soluble in alcohol, they are separated 

 out immediately, leaving the other constituents behind. The alcohol is filtered 

 and mixed with absolute ether until a precipitate is formed. On cooling, the bile 

 salts crystallize out, but since they absorb water very readily, they should be kept 

 in a desiccator. The glycocholic acid may be hydrolyzed by dilute acids and alkalies 

 and split into glycerin or amino-acetic acid and cholic acid. 



C 26 H 43 NO 6 + H 2 O = CH,(NH 2 )COOH + C 24 H 4 oO 8 



(Glycocholic acid) (Glycine) (Cholic acid) 



In the same way taurocholic acid may be split into taurine, or amino-ethyl-sul- 

 phonic acid and cholic acid. 



C 26 H 45 NO 7 S + H 2 = CH 3 CH(NH 2 )S0 2 -OH + C 24 H 40 O 5 



(Taurocholic acid) (TaurineJ (Cholic acid) 



It will be shown later on that the bile salts stimulate peristalsis and serve as 

 a vehicle for the digestion of the fats. Their function having been completed, a 

 portion of them is destroyed through the influence of the intestinal microorganisms, 

 while another portion is again absorbed and returned to the liver by way of the 

 portal blood stream. The hepatic cells rebuild this material into new bile salts, 

 thereby greatly reducing their work in synthetizing these salts. A similar "cir- 

 culation of the bile" between the intestine and the liver is had in the case of some 

 of the derivatives of the pigmentous material of the bile. 



Cholic or cholalic acid is a white, crystalline and very bitter substance which 

 is almost insoluble in water, but soluble in alcohol. On addition of water it crys- 

 tallizes from the latter in rhombic pyramids and tetrahedrons. It is closely allied 

 to cholesterol and may be derived from this substance. 



Cholesterol has been found in the bile of almost all animals, but is not present in 

 considerable amounts in human bile (1.6 in 1000 parts). Since it is insoluble in 

 water and solutions of salts, it must seem peculiar that it is dissolved by the bile 

 and may be present here in even greater amounts than normal. This excessive 

 solvent action of bile is due to its content in bile salts and more particularly to the 



1 Platner, Ann. der Chemie und Pharmazie, li, 1844, 105. 



