COLORING MATTERS. 99 



in the liver, aad may be extracted from its tissue in a pure form. 

 From the liver cells it is taken up by the biliary ducts and mingled 

 with the other ingredients of the bile. It is crystallizable, soluble in 

 chloroform, less so in alcohol, and slightly soluble in ether. It is readily 

 soluble in alkaline liquids, but quite insoluble in pure water. In the 

 crystallized form it is red ; in the amorphous condition, orange ; and in 

 solution, reddish-brown or yellow, according to the degree of concen- 

 tration. According to Hoppe-Seyler, it gives a perceptible yellow 

 color when viewed in a layer 1.5 centimetre in thickness, even if dis- 

 solved in 500,000 times its weight of fluid. 



Solutions of bilirubine exhibit a well-marked reaction with nitroso- 

 nitric acid, known as " Gmelin's bile test." If such a solution be 

 treated with a small quantity of nitric acid, tinged with nitrous acid, 

 a series of colors is presented in the following order : green, blue, 

 violet, red, and finally a dingy yellow. These colors are produced by 

 transformation of the bilirubine, and represent successive degrees of 

 its oxidation. The reaction is a very sensitive one, and, according to 

 Hoppe-Seyler, will produce a visible result in solutions containing only 

 one part in 70,000. 



Bilirubine is generally regarded as derived from hemoglobine. The 

 reasons for this opinion are : First, its reddish color, somewhat simi- 

 lar to that of diluted blood. Secondly, it has been found in various 

 parts of the body, in old bloody extravasations, evidently produced 

 from an alteration of the blood upon the spot. When found under 

 these circumstances, it was formerly known as heniatoidine. Thirdly, 

 if the blood-globules be made to assume a liquid form by alternately 

 freezing and thawing a portion of freshly drawn blood, and this blood 

 then re-injected into the blood-vessels, the operation is followed by a 

 discharge of bilirubine in the urine. If hemoglobine be, in fact, nor- 

 mally transformed into bilirubine, its iron and sulphur must enter into 

 some other combination, as neither of these elements exists in the 

 coloring matter of the bile. Bilirubine, if exposed to the air in alkaline 

 solution, becomes oxidized and assumes a green color, being converted 

 into the following closely related substance, biliverdine. 



4. Biliverdine, C 16 H 20 N,O 5 . 



In addition to bilirubine, the bile contains a green substance, known 

 as biliverdine ; and the varying tint of different specimens of bile 

 depends on the proportion in which the two coloring matters are pres- 

 ent. In man and the carnivorous and omnivorous animals, the bile is 

 bronze, brown, yellowish, or orange, owing to the presence of biliru- 

 bine ; while in the ox, sheep, rabbit, and vegetable feeders generally, 

 it presents a strong green or greenish color, due to the comparative 

 abundance of biliverdine. Biliverdine is insoluble in water, ether, and 

 chloroform, readily soluble in dilute alkaline solutions and in alcohol. 

 It is also soluble in glacial acetic acid, and is deposited from the evap- 

 orated solution in a form of imperfect crystallization. It is often 



