266 THE URINE. 



amount of the chromogen present. In normal urine a faint reaction 

 only is usually seen ; but in disease, and notably in ileus, peritonitis, 

 and cancer of the stomach, I have repeatedly met with more indigo- 

 red than indigo-blue. 



ROSENBACH'S REACTION. This reaction is mostly obtained under 

 pathological conditions, and indicates the existence of greatly in- 

 creased intestinal putrefaction. It is referable to the simultaneous 

 formation of indigo-red and indigo-blue. 



"While boiling, a few cubic centimeters of urine are treated drop 

 by drop with concentrated nitric acid containing a little nitrous 

 acid, when in the presence of much indigo-red, viz., its chromogen, 

 the urine assumes a dark Burgundy color, and usually shows a 

 bluish tint when held to the light. On standing, the red pigment 

 is precipitated. If much indigo-blue is present at the same time, 

 as is usual, the foam of the liquid is colored blue. On adding an 

 excess of the acid the color often disappears and the urine turns 

 yellow. 



The isolation of indican from urine as such is a rather complicated 

 process, and need not be described at this place. 



Quantitative Estimation. WANG'S METHOD (modified by Ellinger). 

 This method is based upon the decomposition of the indican by 

 strong hydrochloric acid, and the oxidation of the resulting indoxyl 

 to indigo-blue. This is then transformed into indigo-sulphuric 

 acid, and estimated as such by titration with a solution of potassium 

 permanganate of known strength. To this end, a stock solution of 

 the salt is kept on hand, which contains about 3 grammes to the 

 liter. Five c.c. of this solution are diluted with 195 c.c. of water, 

 when the titre is ascertained before each titration by comparing it 

 with a dilute solution of oxalic acid. The amount of indigo-blue 

 which each cubic centimeter represents is ascertained by multiplying 

 the corresponding amount of oxalic acid by 1.04. 



The amount of urine which is necessary varies with the amount 

 of indican present. If a preliminary test gives an intense reaction, 

 from 25 to 50 c.c. are sufficient ; otherwise it is better to use larger 

 amounts, as from 200 to 250 c.c. The urine, which should be acid, 

 is then precipitated with a 20 per cent, solution of basic lead acetate, 

 care being taken to avoid an excess. A large portion of the filtrate, 

 representing a known amount of urine, is then treated with an 

 equal volume of Obermayer's reagent, and extracted with chloro- 

 form by shaking. This is continued with portions of 30 c.c. until 

 the chloroform takes up no more coloring-matter. The combined 

 extracts are freed from chloroform by distillation. The residue is 

 dried for a few minutes on a water-bath, and is then washed with 

 hot water. The solution is passed through a small filter, so as to 

 collect any particles of the blue pigment which may be present in 

 suspension. The filter is dried, extracted with boiling chloroform, 

 and the resulting solution filtered into the flask containing the 

 residual indigo-blue. The chloroform is distilled off, and the resi- 



