192 THE SECRETIONS: 



of urine coloured dark by biliphsein, that it exhibits in thin 

 layers a characteristic saffron yellow colour. The presence of 

 biliphsein may be at once detected with certainty by the addi- 

 tion of nitric acid, by which the well-known transitions in 

 colour, from green to violet, red, and yellow are produced. 

 It is only when there is a considerable quantity of biliphsein 

 present that these transitions can be distinctly observed, and 

 the best method of proceeding is to pour a layer of urine care- 

 fully over nitric acid, and to continue the mixture of the two 

 fluids gradually. 



When the quantity of biliphsein is very small, the only 

 changes that we are certain to observe on the addition of the 

 nitric acid, are the transition of the yellow colour of the urine 

 into green, which usually reverts to a yellow, without the 

 intermediate colours being observed. Hydrochloric acid con- 

 verts the yellow or brown colour of the urine into green, but 

 does not develop the other tints. 



An exact quantitative determination of the biliphsein in urine 

 appears, with our present resources, hardly practicable, for its 

 amount is usually very minute, and, like the animal colouring 

 matters generally, it possesses the property of combining very 

 intimately with other constituents. Thus we find uric acid, 

 when it occurs as a sediment in icteric urine, mucus, the ex- 

 tractive matters, &c. always tinged yellow by biliphsein. We 

 must therefore be content, in our estimation of the amount of 

 the biliphsein, to draw our inferences from the intensity of the 

 colour of the urine, and from the degree of change that it 

 undergoes on the addition of nitric acid. 



7. Ellin and bilifellinic acid. 



The quantity of bile in urine is occasionally so large as to 

 communicate to that fluid a decidedly bitter taste : in these cases 

 biliphsein is always present. Whenever biliphsein occurs in 

 urine, we are justified in suspecting the presence of bilin and 

 bilifellinic acid, although they are not always found. 



When the taste of the urine does not decidedly indicate the 

 presence of bilin and of the acids of the bile, we must, in order 

 to be assured of their existence, evaporate the urine, extract the 

 residue with anhydrous alcohol, and then expel the alcohol by 



