BLOOD AND LYMPH. 569 



removed. The large deposits of iron in the liver indicate the extent to 

 which this process has taken place. Bilirubin is not the only pigment 

 present in the bile. . Oxidation products are likewise present which 

 represent different stages to which bilirubin has been oxidized. We need 

 not mention their names here, partly because their relations to bilirubin 

 are not very well known, and partly because it is hard to decide which of 

 these colored substances are previously formed in the cell and which 

 result from secondary processes. The best known of these substances is 

 biliverdin, which may be readily prepared from bilirubin by allowing an 

 alkaline solution of it to stand in contact with the air. Oxygen is 

 absorbed, and the solution turns green. One of the tests for the biliary 

 pigments, the so-called Gmelin's test for bile-pigments, is based upon the 

 readiness with which bilirubin is oxidized. If a solution of bilirubin- 

 alkali is cautiously covered in a test tube with a little nitric acid con- 

 taining some nitrous acid, color rings appear at the contact surface of the 

 two liquids and in the following order from top to bottom : green, 

 blue, violet, red, and reddish-yellow. These different colors are due to 

 different stages resulting from the oxidation of bilirubin. Before con- 

 sidering the subsequent destiny of the bile-pigments, we must answer the 

 question whether the liver is, under normal conditions, the only organ in 

 which the bile-pigments are formed, or whether it is not perhaps merely 

 the place where these pigments are eliminated. 



Even Virchow * recognized the fact that peculiar transformations take 

 place in blood extravasations. The protein component of the hemo- 

 globin and the remaining constituents of the blood disappear as such, 

 and there remain beautifully formed crystals of brick-red to ruby-red 

 color. They are known as hematoidin. This substance contains no 

 iron, and is considered by many to be identical with bilirubin. According 

 to our present knowledge, nothing further can be said concerning this 

 pigment than that it is closely related to hematin and to hematopor- 

 phyrin. Besides this pigment we will state that pigments containing 

 iron have also been observed as being formed in the tissues, and that 

 there has been a constant endeavor to trace a relationship between all 

 the animal pigments, whether resulting from normal or from pathological 

 processes, to the blood-pigment. The most pronounced characteristic 

 that has been noted, however, in every case is as regards the presence or 

 absence of iron. We would refer merely to what was said in considering 

 the formation of hematoidin to show that the iron content in no way 

 indicates the origin of the pigment. Our knowledge in this direction is 

 still far too limited for us to predict much concerning the relations of the 

 animal pigments to the other compounds found in the tissues. 



1 Virchow's Arch. 1, 379 and 407 (1847). 



