684 PHYSIOLOGICAL CHEMISTRY. 



hydrogen sulphide, and evaporate to a small volume. The leucine which is 

 precipitated on standing is best separated from the mother-liquor by placing 

 the mass on a plate of porous clay. Use the crystals to make reactions for 

 leucine (see Index). 



Bile, secreted by the liver, is a thin, transparent liquid of a golden- 

 yellow color, and a specific gravity of 1.020 ; it has a very bitter taste 

 and an alkaline reaction ; it varies widely in composition, the total 

 solids ranging from 9 to 17 per cent., being always highest after a 

 meal ; its composition, moreover, is highly complex ; the following is 

 an average of five analyses of bile from subjects with healthy livers : 



Water 91.68 per cent. 



Mucus and pigment 1.29 " 



Taurocholate of sodium 0.87 



Glycocholate of sodium 3.03 " 



Fat . 0.73 



Soaps . . 1.39 " 



Cholesterin 0.35 " 



Lecithin 0.53 



Bile obtained after death is of a brownish-yellow color ; freed from 

 mucus it will remain undecomposed for an almost indefinite period. 

 The mucus may be separated by the addition of diluted alcohol and 

 subsequent filtration. 



The quantity of bile discharged daily by a grown person may be 

 put at from 1000 to 1700 c.c., or from 23 to 47 ounces, but a con- 

 siderable quantity of this discharged bile is reabsorbed in a changed 

 form by the intestines; only a small amount of bile matters (in a 

 decomposed state, however) is contained in the feces. 



Bile is to be regarded both as a secretion and an excretion, as will 

 be seen below in the statements concerning its constituents. It has 

 long been believed that bile is an intestinal antiseptic. Its action is, 

 however, weak and probably unimportant, as it has been found that 

 certain bacteria (B. typhosus, B. coli) grow well in media containing 

 bile. 



Biliary pigments. Several pigments have been found in bile, but 

 it is probable that only two, bilirubin and biliverdin, occur in normal 

 bile. 



The bile-pigments are formed in the liver from haemoglobin by a 

 process in which the iron is split off and retained in the organism. 

 While the pigments of the bile are regarded as waste products of 

 metabolism, a certain portion of them is absorbed in the intestine, is 

 excreted again by the liver, and also by the kidneys (as urochrome 

 and urobilin). That portion which passes out with the feces is re- 

 duced to stercobilin (isomeric with urobilin). 



