THE LIVER. 153 



greenish color to the bile, or when, as is most frequently the case in 

 ox-bile, the two pigments are present in the bile at the same time, 

 producing the different shades between reddish brown and green. 



Bilirubin. This pigment, according to the common accepta- 

 tion, has the formula C 16 H 18 N 2 3 (MALT) and is designated by the 

 names CHOLEPYRRHI^, BILIPHJEIN, BILIFULVIN and H^EMATOIDIN. 

 It occurs chiefly in the gall-stones as bilirubin-calcium. It is further 

 found in the bile, especially in man and carnivora ; sometimes, 

 however, the latter when fasting or in a starving condition may 

 have a green bile in the gall-bladder. It occurs also in the contents 

 of the small intestines, in blood-serum of the horse, in old blood 

 extravasations (as haematoidin), and in the urine and the yellow- 

 colored tissue in icterus. The bilirubin is in all probability a forma- 

 tion from the haematin which it closely resembles. It is converted 

 into hydrobilirubin, Cg.}!!^^ (MALY), by hydrogen in a nascent 

 state. It is claimed by several investigators to be identical with the 

 urinary pigment urobilin, as well as with stercobilin (MASIUS and 

 VANLAIR), which is found in the contents of the intestines. There 

 is no doubt that a great similarity exists between these pigments, 

 but their identity is emphatically denied by MAcMuNN. On oxida- 

 tion bilirubin yields biliverdin and other coloring matters (see below). 



Bilirubin is partly amorphous and partly crystalline. The 

 amorphous bilirubin is a reddish-yellow powder of nearly the same 

 color as amorphous antimony sulphide; the crystalline bilirubin has 

 nearly the same color as crystallized chromic acid. The crystals, 

 which can easily be obtained by allowing a solution of bilirubin in 

 chloroform to spontaneously evaporate, are reddish-yellow, rhombic 

 plates, whose obtuse angles are often rounded. 



Bilirubin is insoluble in water, slightly soluble in ether, some- 

 what more soluble in alcohol, easily soluble in chloroform, especial- 

 ly in the warmth, and less soluble in benzol, carbon disulphide, amyl 

 alcohol, fatty oils, and glycerin. Its solutions show no absorption- 

 bands, but only a continuous absorption from the red to the violet 

 end of the spectrum, and they have, even on diluting greatly, 

 (1 : 500000) a decided green color. The combinations of bilirubin 

 with alkalies are insoluble in chloroform, and bilirubin may be 

 separated from its solution in chloroform by shaking with dilute 

 caustic alkali (differing from lutein). Solutions of bilirubin-alkali 



