APPENDIX. 685 
acid it undergoes a series of oxidations, giving rise to distinct products 
of which one is the green biliverdin. These oxidations are the basis of 
Gmelin’s test for bile-pigment, which consists in adding a drop of strong 
nitric acid containing nitrous acid to bile, when a series of rather rapid 
changes in color in a certain order takes place. 
Biliverdin. C,>HisN2O,. 
It is this pigment which gives the characteristic color to ox-gall, from 
which it is best prepared. It is not soluble in ether or chloroform, but 
dissolves readily in alcohol. 
In all probability both the bile-pigments and their derivatives are 
the result of the final transformations of hemoglobin. 
Choletelin. CasHieNaOc. 
This is the final product of the oxidation of bilirubin. 
Hydrobilirubin. CsaHsoN.Or. 
When an alkaline solution of bilirubin is acted upon by sodium amal- 
gam, the above results. It is thought by many to be identical with ster- 
cobilin, a product of the decomposition, etc., of bile in the intestine. Since 
hydrogen in the nascent condition probably occurs in the intestines as 
the result of fermentations, the conditions for the formation of this sub- 
stance seem to be met. 
Pigments of Urine. 
It seems to be‘more than probable that the urine contains a great 
number of pigments. But few of these, however, have been isolated. 
The best known are the following: 
Urobilin. CssHsN.sOv. 
The formule of all these bodies are but indifferently known. 
Urobilin is thought to be identical with hydrobilirubin. It is pres- 
ent, but in small quantities, in normal urine, though often largely in the 
urine of febrile conditions. It is supposed to be an oxidized form of 
chromogen. 
Uroerythrin. 
Supposed to abound in the urine of rheumatic patients. It becomes 
greenish on addition of caustic alkali, and reddish or reddish-yellow when 
concentrated hydrochloric acid is added. 
The Indigo Series. 
Indican. C2cHs:NOn. 
Some regard indican as indoxyl! sulphuric acid, which does not occur 
in the free state, but as a salt of potassium. It represents in the urine 
the indol of the alimentary canal. 
Indigo. CyeHioNsOz. 
It occasionally occurs in sweat and urine as an oxidation product of 
indican. 
It may be obtained from human urine, and still more readily from 
that of the herbivora, by the cautious addition of a weak solution of 
