160 THE DIGESTIVE FLUIDS. 



icterus. At the same time the bile-acids bring about a dissolution 

 of the red corpuscles, and thus manifest their true nature as excretory 

 products. 



Regarding the origin of the biliary acids, we know only that 

 they are formed exclusively in the liver, but of the manner in 

 which their formation takes place we are ignorant. 



The amido-radicles of the bile-acids are unquestionably formed in 

 the general nitrogenous metabolism of the body, and, as such, are 

 found in other organs besides the liver. Glycocoll is then to a cer- 

 tain extent further oxidized, and contributes to the formation of 

 urea. Of the ultimate fate of taurin, we know that its sulphur can 

 be oxidized to sulphuric acid and be eliminated in the urine in this 

 form. In the human being traces are further excreted as tauro- 

 carbaminic acid ; and in rabbits, at least, its hypodermic injection 

 leads to the elimination of the body as such. It is thus difficult to 

 understand why two substances like these, for the removal of which 

 the animal body has manifestly other means at its disposal than 

 their elimination through the bile, should here appear. We may 

 imagine, however, that the formation of the bile-acids in the liver 

 represents a conservation of energy on the part of the body, and 

 further constitutes a reserve mechanism by which waste-products 

 can be removed in a state of incomplete oxidation. 



Of the origin of the non-nitrogenous acids, which combine with 

 glycocoll and taurin to form the biliary acids, we know nothing. 

 The synthesis, however, manifestly occurs in the liver, and here 

 only, as after extirpation of the organ in birds and frogs bile-acids 

 are not found in the blood. In mammals, also, neither bile- 

 pigments nor bile-acids can here be demonstrated after ligating the 

 biliary duct and the thoracic duct. 



In the bile of most animals the biliary acids occur in combination 

 with sodium, while in sea-fish they are, curiously enough, present as 

 potassium salts. 



As regards the relative quantity of the two principal biliary acids 

 which are found in the bile, it is to be noted that in man glycocholic 

 acid is usually more abundant than taurocholic acid. In strictly 

 carnivorous animals, on the other hand, the latter only is found; 

 but the same also holds good for certain herbivora, such as the sheep 

 and the goat. In other animals the relation is variable, and in 

 some, it is stated, glycocholic acid only is found. 



Isolation. Collectively, the biliary acids, in the form of their 

 salts, can be obtained in the following manner : the bile is mixed 

 with animal charcoal, evaporated to dryness, and the residue ex- 

 tracted with absolute alcohol. This extract, which contains the 

 biliary acid salts, cholesterin, fats, soaps, and lecithin, is then 

 filtered, concentrated, and treated with a large excess of ether. In 

 this manner the salts of tho bile-acids are precipitated, while the 

 other substances remain in solution. On standing, the precipitate 

 gradually becomes crystalline, and is then spoken of as Platner's 



