444 EXCRETION. 



is that it is a neutral fatty substance extracted from the bile, and is capable of being 

 decomposed into phosphoric acid and glycerine. Choline is a peculiar alkaloid found in 

 the bile in exceedingly minute quantity. 



Biliary Salts. The principles which we have called biliary salts are compounds of 

 soda with peculiar organic acids, found nowhere but in the liver, and undoubtedly pro- 

 duced in this organ from materials furnished by the blood. The fact that the bile pos- 

 sesses peculiar principles has long been recognized. It is unnecessary, however, to 

 follow out in detail the earlier chemical investigations into their properties; for the 

 biliary matter of Berzelius and the picromel and biliary resin of Thenard are now known 

 to be composed of several distinct proximate principles. Our exact knowledge of these 

 substances dates from the analyses of ox-bile by Strecker. He obtained two peculiar 

 acids, cholic and choleic acid, which he found in the bile, in combination with soda. In 

 the subsequent researches of Lehmann, these acids are called, respectively, glycocholic 

 and taurocholic acid, and the salts, glycocholate and taurocholate of soda. 



In human bile, the proportion of glycocholate of soda is very small, the biliary mat- 

 ter existing almost entirely in the form of the taurocholate. The taurocholate may be 

 precipitated from an alcoholic extract of bile by ether, in the form of dark, resinous 

 drops. These do not crystallize, and the amount of glycocholate, which is precipitated 

 in the same way and soon assumes a crystalline form, is very slight. Prof. Dalton, who 

 has studied the biliary salts very closely, at first was unable to obtain any crystalline 

 matter from human bile, but he has lately found it in minute quantity. 



Taurocholate of Soda. There is some doubt whether the resinous drops obtained by 

 the addition of an excess of ether to a strong alcoholic extract of bile consist of a proxi- 

 mate principle in a perfectly pure state. These drops are not crystallizable, and this has 

 led to the opinion that they are impure. In fact, even now, there is a certain amount of 

 obscurity with regard to the character of these peculiar biliary salts. In ox-bile, the 

 non-crystallizable and the crystallizable salts exist together ; but, in human bile, the 

 greatest part is in the form of what we know as the taurocholate of soda. 



These salts may be readily obtained from ox-bile and separated from each other by 

 the following process : The bile is first evaporated to dryness and pulverized. The dry 

 residue is then extracted with absolute alcohol and filtered. In this part of the process, 

 Dr. Dalton uses five grains of the dry residue to one fluidrachm of alcohol. The filtered 

 fluid is of a clear, yellowish color, and it contains fats and coloring matter, in addition to 

 the biliary salts. To precipitate the biliary salts, a small quantity of ether is added, 

 which produces a dense, white precipitate that redissolves by agitation. Another small 

 quantity of ether is again added, and the precipitate thus produced is dissolved by shak- 

 ing the mixture. This process is repeated carefully, adding the ether and shaking the 

 mixture after each step, until the precipitate becomes permanent. An excess of ether 

 from eight to ten times the bulk of the alcoholic extract used is then added, the test- 

 tube or flask is carefully corked, and the mixture is set aside to crystallize. Gradually 

 the dense, white precipitate falls to the bottom of the vessel or becomes attached in the 

 form of resinous drops to the sides of the glass ; and in from six to twenty-four hours it 

 begins to form delicate, acicular crystals, arranged in rosettes. These are crystals of the 

 glycocholate of soda ; and the non-crystallizable matter remaining is the taurocholate of 

 soda. 



To separate the biliary salts from each other, the ether is rapidly poured off, and the 

 crystalline and resinous residue is dissolved in distilled water. On the addition to this 

 solution of a little acetate of lead, the glycocholate is decomposed and precipitated in the 

 form of glycocholate of lead, leaving the taurocholate in solution. The glycocholate of 

 lead is then separated by filtration, and the subacetate of lead is added to the filtered 

 fluid. This decomposes the taurocholate, and the taurocholate of lead is precipitated. 

 The subacetate of lead will decompose both the glycocholate and the taurocholate, but 



