PIGMENTATION. 57 



is liable. The most important of these, and in some sense 

 typical of all the rest, is its transformation into bile-pigment. 

 This phenomenon, however plausible a j^rmri, has long been 

 shrouded in mystery. It seemed hazardous, and very justly so, 

 to derive a chemical substance produced exclusively by the 

 activity of the hepatic cells, from a certain constituent of the 

 blood, solely on the ground of its possessing like optical pro- 

 perties. At the present day these scruples have lost all meaning, 

 and that mainly in consequence of the following observations. 

 In places where blood has some time previously been extrava- 

 sated, hgematoidin is not unfrequently found in the form of small, 

 fiery-red crystals, belonging to the rhombic system (fig. 20). 

 There can be no doubt that this hsema- 

 toidin is derived from the blood-pigment ; I^ig- 20. 



and yet it differs from hsematin in containing ^ /^^ frl 

 no iron. When treated with powerful oxi- "^^T^ ^ 



dising agents, such as concentrated sulphuric (<^3H \V 

 acid, it gives a play of prismatic colours. [^^ 

 It need hardly be said that these very ^^^ 



i^roperties by which hsematoidin is distin- Crystals of Hjema. 

 . T , p , , . ^1 toidm (after Vir- 



guished from the colounng matter or the diow). 



blood, bring it nearer to bile-pigment. This 

 alone made it highly probable that bile-pigment ought to be 

 regarded as derived from the colouring matter of the blood ; and 

 this probability became a certainty when Valentiner discovered 

 that hsematoidin could be extracted from dried and powdered 

 bile by means of chloroform. Now, it is quite true that a 

 crystalline pigment may be obtained in this manner, not dis- 

 tinguishable at first sight from haimatoidin. Nevertheless Valen- 

 tiner\s discovery had to submit to a slight correction. Stddeler 

 found that the crystalline colouring matter of the bile (bili- 

 rubin, CggHigNgOg) difl^ered from haematoidin (CgoHigNgOg, 

 Eohhi), not only by a trifling variation in the angular measure- 

 ment of its crystals, but also in containing two atoms more 

 carbon. Stddeler, however, considers this difference as too insig- 

 nificant to shake the proposition that bile-pigment is derived 

 from blood-pigment. The red corpuscles, as they grow old, 

 part with their colouring-matter to the serum ; from this it is 

 taken up by the liver-cells, which transform it into bile-pigment ; 

 as such it is ultimately excreted in the fseces. Before it is 



