172 THE DIGESTIVE FLUIDS. 



On reduction with nascent hydrogen bilirubin is transformed into 

 urobilin, as is shown by the equation : 



viz., 2C 16 H 18 N 2 O 3 ) + H 2 O + 2H = C 32 H 40 N 4 O 7 



Urobilin. 



This actually takes place in the intestinal canal, where nascent 

 hydrogen is constantly being formed through the action of various 

 bacteria, as during the process of lactic acid fermentation. During 

 intra-uterine life, however, where no bacteria are found in the 

 intestinal tract, bilirubin appears in the feces as such (meconium). 



In the crystalline state bilirubin occurs in the form of reddish- 

 yellow rhombic platelets with rounded angles, which are soluble in 

 benzol, carbon disulphide, amyl alcohol, glycerin, the fatty oils, and 

 especially in warm chloroform. In alcohol and ether they are but 

 little soluble, and in water, as also in Platner's bile, they are insol- 

 uble. On spectroscopic examination its solutions do not give rise to 

 any specific bands of absorption, but to a continuous absorption 

 which extends from the red to the violet end. 



Bilirubin as such is a weak acid, bilirubinic acid, and combines 

 with bases to form salts, which for the most part are either insoluble 

 or only slightly soluble in water and insoluble in chloroform. Its 

 salts with the alkalies, however, are soluble in solutions of the alka- 

 line hydrates and carbonates. In the bile bilirubin is largely present 

 as neutral bilirubinate of sodium, and is held in solution owing to 

 the presence of alkaline carbonates. 



When perfectly fresh bile of a golden-yellow or olive-brown color 

 is exposed to the air for a while, it will be noted that the fluid grad- 

 ually assumes a bright-green color, owing to a transformation of the 

 bilirubinate into biliverdinate of sodium. Free bilirubin, according 

 to Dastre and Floresco, does not absorb oxygen and is thereby 

 transformed into biliverdin, as has been supposed. The same 

 observers state that on careful oxidation bilirubin can be trans- 

 formed into biliprasin, which presents a green color as such, while 

 its sodium salt, sodium biliprdsinate, is yellowish brown. On 

 further oxidation the biliprasin then yields biliverdin, viz., its cor- 

 responding salt. 



According to former views, the relation existing between bilirubin 

 and biliprasin were represented by the equations given below ; but 

 it is, of course, manifest that these are no longer tenable if the work 

 of Dastre and Floresco should be confirmed. 



C 16 H 18 N 2 3 + = C 16 H 18 N 2 4 



Bilirubin. Biliverdin. 



C 16 H 18 N 2 3 + H 2 = C 16 H 20 N 2 4 

 Bilirubin. Bilifuscin. 



C 16 H 20 N 2 4 + H 2 + O = C 16 H 22 N 2 6 

 Bilifuscin. Biliprasin. 



The formula of biliprasin, as here indicated, would, moreover, be 

 an impossibility. As a matter of fact, these formula? cannot be 



