204 PHYSIOLOGICAL CHEMISTRY 



bladder or by means of a fistula before it reaches the gall-bladder. 

 The variation in the composition of these two types of bile is shown in 

 the preceding selected analyses : 



The bile acids, which are elaborated exclusively by the hepatic 

 cells, may be divided into two groups, the glycocholic acid group and 

 the taurocholic acid group. In human bile glycocholic acid predomi- 

 nates, while taurocholic acid is the more abundant in the bile of car- 

 nivora. The bile acids are conjugate amino-acids, the glycocholic 

 acid yielding glycocoll, 



CH 2 -NH 2 



I 

 COOH, 



and cholic acid upon decomposition, whereas taurocholic acid give 

 rise to taurine, 



CH 2 -NH 2 



I 

 CH 2 -S0 2 -OH, 



and cholic acid under like conditions. Glycocholic acid contains some 

 nitrogen but no sulphur, whereas taurocholic acid contains both these 

 elements. The sulphur of the taurocholic acid is present in the taurine 

 (amino-ethyl-sulphonic-acid) , of which it is a characteristic constituent. 

 There are several varieties of cholic acid and therefore we have several 

 forms of glycocholic and taurocholic acids, the variation in constitution 

 depending upon the nature of the cbolic acid which enters into the com- 

 bination. The bile acids are present in the bile as salts of one of the 

 alkalis, generally sodium. The sodium glycocholate and sodium tau- 

 rocholate may be isolated in crystalline form, either as balls or rosettes 

 of fine needles or in the form of prisms having ordinarily four or six 

 sides (Fig. 55, page 205) . The salts of the bile acids are dextro-rotatory. 

 Among other properties these salts have the power of holding the 

 cholesterol and lecithin of the bile in solution. 



Hammarsten has demonstrated a third group of bile acids in the 

 bile of the shark. This same group very probably occurs in certain 

 other animals also. These acids are very rich in sulphur and resemble 

 etheral sulphuric acids inasmuch as upon treatment with boiling hydro- 

 chloric acid they yield sulphuric acid. 



The bile pigments are important and interesting biliary constitu- 

 ents. The following have been isolated: bilirubin, biliverdin, bili- 

 fuscin, biliprasin, bilihumin, bilicyanin, choleprasin, and choletelin. Of 

 these, bilirubin and biliverdin are the most important and predominate 

 in normal bile. The colors possessed by the various varieties of normal 

 bile are due almost entirely to these two pigments, the biliverdin being 



