THE BILE. 173 



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 biliverdin Kiister obtained a new oxi- 

 dation-product, which he termed bUiverdmic 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 identical with 

 the dibasic hsematinic acid, which results from hsematin directly, 

 and, like this, yields a substance of the composition C 8 H 8 O 5 , viz., 

 the anhydride of the dibasic hsematinic acid, C 8 H 1( jO 6 . 



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

 is treated with an amount of concentrated nitric acid, containing a 

 trace of nitrous acid, sufficient to form a layer beneath the liquid to 

 be tested, when in the presence of bilirubin a color- play from yellow 

 tli rough green, blue, violet, and red to orange will be observed at the 

 zone of contact ; the green will be noticed nearest the bile-containing 

 solution, and the orange in the upper portion of the nitric acid. 



The test is exceedingly sensitive, and is said to indicate the pres- 

 ence of bilirubin in a dilution of 1 : 80,000. The green color which 

 develops is the most characteristic, but a reddish violet must also 

 occur. 



ROSENBACH'S MODIFICATION OF GMELIN'S TEST. If bile contain- 

 ing 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, the play of colors 

 just described will occur. The green color is referable to the bili- 

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

 and the final orange to choletelin. 



HUPPEKT'S TEST. A few cubic centimeters of the solution to 

 be examined are precipitated with barium chloride and ammonia. 

 The precipitate is washed with water and suspended in a small 

 amount of alcohol that has been acidulated with sulphuric acid. 

 This mixture is then boiled for a few minutes, when in the presence 

 of bilirubin a bright emerald-green color develops. 



SMITH'S TEST. A small amount of the fluid is placed in a test- 

 tube and treated with a few cubic centimeters of tincture of iodine 

 which has been diluted with alcohol in the proportion of 1 : 10, so 

 as to form a layer above the fluid to be examined. In the presence 

 of bilirubin a distinct emerald-green ring will develop at the zone 

 of contact. 



According to some observers, the green color which thus results 

 when bilirubin is treated with iodine is not referable to the forma- 

 tion of biliverdin, but to a substitution- or addition-product of bili- 

 verdin with iodine. This, however, is denied by others, and Jolles 

 has shown that the iodine merely acts as an oxidizing agent, and 

 that true biliverdin is formed, as indicated by the equation : 



C I(J H 18 N 2 3 -f 21 + H 3 = C, 6 H 18 N 2 4 + 2HL 



