1304 BILIRUBIN. 



Bile-pigments are also stated to occur normally in the urine of 

 dogs, more particularly in the summer. 



Bilirubin is insoluble in water and almost insoluble in 

 either ether or alcohol, though distinctly more soluble in 

 alcohol than in ether. It is on the other hand readily soluble 

 in alkaline solutions, hence its solution in bile, also in glycerin 

 carbon-disulphide, and benzene, and above all in chloroform. 

 From its solution in the latter it may be separated out by 

 extremely slow evaporation of the solvent in a crystalline form 

 as rhombic plates or prisms. The general shape of these 

 is shewn above in Fig. 233; but as obtained from solution in 

 either carbon-disulphide or chloroform the crystals usually 

 exhibit somewhat blunt ends and slightly convex surfaces. As 



Fig. 234. Bilirubin crystallized from Carbon-disulphide. (Krukenberg.) 



ordinarily prepared it is an amorphous powder of the colour of 

 sulphide of antimony. It readily forms compounds with bases, 

 e.g. sodium, barium and calcium, the latter providing a con- 

 venient means for the separation of bilirubin from bile, urine 

 or other dilute solution. 



When carnivorous bile is exposed to the air it turns more 

 or less rapidly green ; this is due to its oxidational conversion 

 into biliverdin, the normal pigment of herbivorous bile. A 

 similar change is at once produced by an oxidizing agent such 

 as nitric acid containing nitrous acid, but in this case the 

 change of colour does not stop short with green but passes 

 successively through blue, violet and red to a final yellow. 

 These later colours are due to products of the progressive 

 oxidation of the first formed biliverdin, but with the exception 

 of the final substance (choletelin), they are as yet but imper- 

 fectly characterized. The play of colours observed when either 

 bilirubin or biliverdin is oxidized, constitutes the well-known 

 Gmelin's reaction. This is extremely delicate and may be 

 applied in either of the two following ways. A few drops of 

 the suspected solution are placed on a porcelain slab and a drop 

 of yellow fuming nitric acid is brought into contact with it. 

 A play of colours is observed at the junction of the fluids if 

 bile-pigments are present. Or on the other hand some of the 



