PHYSIOLOGY OF THE LIVER AND SPLEEN. 815 



of globin must be formed also, but nothing is known of the fate of 

 this portion of the molecule. Quantitative data are lacking in 

 regard to the amount of bile pigment secreted daily. Owing 

 to the want of a satisfactory method of estimating this sub- 

 stance, its percentage in the bile, as given by different authors, 

 varies greatly, from .04 per cent, to 0.25 per cent. The bile 

 pigments are carried in the bile to the duodenum and are mixed 

 with the food in its long passage through the intestine. Under 

 normal conditions neither bilirubin nor biliverdin occurs in the 

 feces, but in their place is found a reduction product, urobilin, 

 formed in the large intestine, probably in consequence of the 

 activity of the bacteria. Moreover, it is believed that some of 

 the bile pigment is reabsorbed as it passes along the intestine, is 

 carried to the liver in the portal blood, and is again eliminated. 

 That this action occurs, or may occur, has been made probable 

 by experiments of Wertheimer* on dogs. It happens that sheep's 

 bile contains a pigment (cholohematin) that gives a characteristic 

 spectrum. If some of this pigment is injected into the mesenteric 

 veins of a dog it is eliminated while passing through the liver, and 

 can be recognized unchanged in the bile. The value of this "cir- 

 culation of the bile," so far as the pigments are concerned, is not 

 apparent. 



Bile Acids. " Bile acids" is the name given to two organic acids, 

 glycocholic and taurocholic, which are always present in bile, and, 

 indeed, form very important constituents of that secretion; they 

 occur in the form of their respective sodium salts. In human bile 

 both acids are usually found, but the proportion of taurocholate 

 is variable, and in some cases it may be absent altogether. 

 Among herbivora the glycocholate predominates, as a rule, although 

 there are some exceptions ; among the carnivora, on the other hand, 

 taurocholate occurs usually in greater quantities, and in the dog's 

 bile it is present alone. Glycocholic acid has the formula C 26 H 43 NO 6 , 

 and taurocholic acid the formula C 26 H 45 NSO 7 . Each of them can 

 be obtained in the form of crystals. When boiled with acids or alka- 

 lies these acids take up water and undergo hydrolytic cleavage, the 

 reaction being represented by the following equations: 



C^H^NOe + H 2 O = C^H^Os + CH ? (NH 2 )COOH. 



Glycocholic acid. Cholic acid. Glycocoll (amino-acetic-acid). 



C^H^NSO, + H 2 O = CLH^p, + C 2 H 4 NH 2 SO 2 OH 



Taurocholic acid. Cholic acid. Taurin (amino-ethyl- 



sul phonic acid). 



These reactions indicate that the bile acids are probably formed by 

 a reverse process, in the one case by a conjugation of glycocoll with 



* "Archives de physiologie normale et pathologique," 1892, p. 577. 



