DIGESTION IN THE SMALL INTESTINE. 387 



increased by an increase in albuminoid diet, though not in the same 

 degree as occurs in the case of urea. It is rapidly decomposed into 

 taurin and cholic acid ; this decomposition also occurring in the 

 intestine. 



Glycochol (C 3 H s X0 3 ), or glycin, is also formed by boiling gelatin with 

 dilute sulphuric acid. It is a crystallized body, slightly soluble in water, 

 insoluble in alcohol and ether. Its aqueous solutions have a faintly acid 

 reaction. It does not occur as such in the animal body, but, besides 

 being concerned in the origin of the bile acid, it is also found in the 

 urine, especially of the horse, united with benzoic acid in the form of 

 hippuric acid. It may be obtained from the glycocholic acid, as already 

 indicated, by boiling with strong hydrochloric acid. 



Taurin (C a H,NSO a ) occurs in large, glistening columns as a product 

 of splitting of the bile acids. It is readily soluble in water, insoluble 

 in alcohol and ether. It is also found in the intestinal canal and in 

 the flesh of various fish and of the horse, and in the kidneys, spleen, 

 and lungs of various other animals. It is also found in putrid bile, 

 being then developed at the expense of the taurocholic acid in the 

 fermentation of the bile. It combines with various bases to form 

 salts. The bile acids may thus be regarded as compounds of glycochol 

 and taurin with cholic acid, whose chemical composition and general 

 properties are not certainly known. Cholic acid may be regarded, there- 

 fore, as the starting point of the biliary acids. 



Cholic Acid (H 40 C 24 O 5 +H a O).— Cholic acid is a constant product of 

 decomposition of biliary acids, and is therefore found in the intestinal 

 contents, occasionally in the urine of jaundice, but not in fresh bile or 

 elsewhere in the organism. Cholic acid occurs in an amorphous and in 

 a crystallized form; it is insoluble in water, soluble with difficulty in 

 ether, and moderately soluble in alcohol. 



"It may be prepared by boiling bile with caustic potash for twelve to twenty- 

 four hours, then precipitating with hydrochloric acid, and, having washed the 

 deposit with water, dissolving it in caustic soda containing a little ether ; hydro- 

 chloric acid is next added, and after some time crystals form. The supernatant 

 fluid may be decanted, and the residue covered with ether ; dram off the ether in 

 a half-hour or so, and dissolve the deposit in boiling alcohol ; to this solution 

 add a little water until a permanent precipitate appears, and tetrahednc crystals 

 soon make their appearance." 



(c) The Coloring Matters of the Bile.— The bile under different con- 

 ditions and in different animals contains a number of different coloring 

 matters, to' which its different shades of color are due. The essential 

 coloring matter of fresh bile is bilirubin, to which the reddish-brown 

 color of the bile of man and the carnivora is due, and which appears 

 to be the starting point of the various coloring matters which are found 

 in the bile of different animals ; it also occasions the various changes 



