158 THE DIGESTIVE FLUIDS. 



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

 i- exposed to the air tor a while, it will be noted that the fluid grad- 

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

 bilirubinate into bihvtrdinate 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 biliprasinate, 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 0< 



Bilirubin. Biliverdin. 



C 16 K 18 NA + H 2 = C 16 H 20 N 2 4 

 Bilirubin. Bilifuscin. 



C 16 H 20 X 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 

 regarded as definitely established ; and according to some observers, 

 the molecule of biliverdin is only one-half as large as represented 

 above. Much work still remains to be done in this connection, but 

 we know at least that biliverdin constitutes a normal oxidation- 

 product of bilirubin. From biliv^din Kiister claims to have 

 obtained a new oxidation-product, which he termed biliverdinic acid, 

 but which must not be confounded with the substance of the same 

 name referred to above. This body has the formula C 8 H 9 NO 4 , and 

 is apparently identical with the dibasic hsematinic acid, which results 

 from ha3matin directly, and, like this, yields a substance of the com- 

 position C 8 H 8 O 5 , viz., the anhydride of the dibasic hsematinic acid 

 C 8 H 10 O 6 . In this manner the origin of bilirubin from the coloring- 

 matter of the blood is still further shown. 



If bile containing bilirubin is filtered through Swedish filter- 

 paper, and a drop of concentrated nitric acid containing a trace 

 of nitrous acid is placed upon the paper, which is colored a bright 

 yellow, a play of colors will be observed, in which the yellow first 

 turns to green, then to blue, to violet, to red, and ultimately to 

 orange. This reaction is commonly referred to the formation of 

 various oxidation-products of bilirubin, and is very characteristic. 

 The individual products, however, which thus result are mostly but 

 imperfectly known. The green color, of course, is referable to the 

 biliverdin. The blue color is ascribed to bilicyanin or cholecyanin, 

 and the final orange to choletelin. 



Tests for Bilirubin. GMELIX'S TEST. The fluid to be examined 



