124 THE BILE. 



but soluble in ether, chloroform, or hot alcohol. It crys- 

 tallizes from ether in fine, silky needles; from alcohol in 

 large plates containing a molecule of water of crystalliza- 

 tion. (Plate I, 4.) In large quantities it has the appear- 

 ance of a mass of white plates with a pearly luster and a 

 greasy feeling. It is distinguished from the fats by its 

 insolubility in the caustic alkalies, even when boiling. It 

 forms compounds with the fatty acids similar to the fats, 

 the cholesterin taking the place of the glycerin. Lanolin, 

 which is found in wool-fat, is an example. These are not 

 easily decomposed by bacteria, hence can be advanta- 

 geously substituted for the animal fats where decomposition 

 is objectionable. The cholesterin as found in the animal 

 body seems rather to be an excrementitious material than 

 to have any function of its own. 



The bile contains at least two well-characterized pig- 

 ments or coloring matters: bilirubin, C 32 H 36 N 4 G ; and 

 biliverdin, C 32 H 36 N 4 8 . The different colors of bile from 

 a brown to a green are due to a preponderance of one or 

 other of these. They seem to be formed from the blood- 

 coloring matters, being found in old blood-extravasations 

 and being increased in amount in the bile when the blood- 

 corpuscles are destroyed, so that the coloring matters are 

 set free in the plasma. 



Bilirubin occurs in many biliary calculi, particularly 

 in and around the nucleus. This is the best source of the 

 pure substance. It is commonly an amorphous powder, 

 orange-red in color. It is insoluble in water, but can be 

 dissolved in chloroform, and crystallizes from the latter in 

 plates and prisms. It unites with strong bases and in cal- 

 culi occurs in union with calcium. By reduction hydro- 

 bilirubin, C 32 H 40 N 4 7 , is formed. This change takes place 

 in the large intestine as a result of putrefactive action, and 



