BY DR. LAUDER BRUNTON. 495 



lution of biliverdin is used instead of bilirubin, the same 

 changes of color occur, but the first change is of course to 

 blue. In the reaction above described, the oxidation is most 

 complete at the point of contact of the two liquids, the degree 

 of action diminishing as the distance from this point increases. 

 If, therefore, the two liquids as^Hrought into contact without 

 agitation, successive zones of color are formed by the products 

 of oxidation in the same order as befoi*^riz., green, blue, violet, 

 red, and dirty yellow, the last m.entidH|| being nearest the 

 acid. In order to apply the test to a fl urn supposed to contain 

 bile pigment, pour it in a thin layer on a white porcelain plate, 

 and place two or three drops of nitric acid in contact with its 

 edge. Or pour nitric acid containing a little nitrous acid into 

 a test tube: hold it obliquely, and let the fluid to be tested 

 flow gently down the side of the test-tube and over the surface 

 of the acid. Fix the test-tube in the same oblique position, 

 without shaking, in a holder, and let it stand ; see from time 

 to time whether the rainbow-colored zones have appeared at 

 the point of junction in the proper order. Brucke's method is 

 to mix the fluid to be tested with very dilute nitric acid, and 

 then to let a little strong sulphuric acid run gently down the 

 side of the test-tube. Dilute nitric acid alone does not act on 

 the bile pigment, but after the addition of the sulphuric acid 

 the colored rings spread from its upper surface. Ox-gall does 

 not exhibit the colored zones, even when treated with strong 

 nitric acid, unless it contains much nitrous acid. 



To show them, pour a little ox-bile on one part of a porce- 

 lain plate, and on another near it some very strong nitric acid, 

 containing much nitrous acid, or nitric acid, previously mixed 

 with concentrated sulphuric acid and let the bile and acid 

 gently come in contact. 1 



1 When the urine of a patient suffering from jaundice is tested for 

 bile pigments with nitric acid, the color reaction sometimes cannot be 

 obtained, even though the urine be so dark that the foam on its surface, 

 after shaking it, is quite yellow. This negative result generally occurs 

 in cases where the temp-mature of the patient is high/ and more espe- 

 cially when it has continued high for some time, it is then advisable, 

 instead of testing the urine directly with nitric acid, to use the method 

 recommended by Huppert. Precipitate the urine with milk of lime, 

 throw the precipitate on a fluted filter, and allow the fluid to drain siwav. 

 Take a piece of the precipitate, about the size of half a ha/,el-nut, place 

 it in a test-tube, fill the tube half full of alcohol, and then add dilute 

 sulphuric acid in such quantity that the fluid, after being shaken, has an 

 acid reaction. Warm the tube : the tluid will extract the color from the 

 precipitate ; filter and boil the; filtrate. If bilirubin is present in the 

 urine, it will combine with the lime and be precipitated ; but it will be 

 again set free by the su.phuric acid, and be dissolved by the warm aci- 

 ilulated alcohol, forming a yellowish-green solution. This solution will 

 become dark green on boiling, and the more free acid present, the sooner 

 will it do so. When long boiled, it sometimes becomes blue. 



