460 PHYSIOLOGICAL CHEMISTRY. 



porter ; a reddish and smoky tint generally indicates the presence of 

 blood, and a brownish-green suggests the presence of the coloring 

 matter of bile. (Plate VIII., 1-3.) 



The true nature of the normal coloring matters of urine is as yet 

 doubtful ; the existence of at least two has, however, been demon- 

 strated ; they have been named urobilin and urochrome, and are, most 

 likely, products of the decomposition of biliary matters. 



Abnormal coloring matters are chiefly those of blood, bile, and of 

 certain vegetables ; thus, rhubarb and senna leaves cause a reddish- 

 yellow to deep red color, especially in alkaline urine; santonin pro- 

 duces a bright-yellow color, changing to red or crimson on the 

 addition of an alkali. Carbolic acid introduced into the system 

 causes a dark, or even black discoloration of urine, while large doses 

 of salicylic acid color it green. 



The coloring matters of blood may be recognized by adding to a few 

 drops of urine a drop of freshly prepared tincture of guaiacum, and 

 agitating with a solution of ozonized ether (ethereal solution of hydro- 

 gen dioxide) ; the latter is colored blue in case haemoglobin is present. 

 In place of ozonized ether, oil of turpentine which has been in contact 

 with atmospheric air for some weeks may be used, and the test made 

 by allowing urine to flow down the test-tube containing a mixture of 

 the oil and tincture ; a blue coloration will slowly appear, if blood 

 be present. The test has the serious disadvantage that protoplasm in 

 almost any form will give the blue color. 



Detection of biliary coloring matter will be considered later. 



Indican, C 8 H 6 N.HSO 4 . This substance is pale-yellow, but yields 

 readily blue indigo by oxidation. It occurs in very small quantities 

 in normal urine, but is much increased in cases of marked intestinal 

 fermentation, also in abdominal diseases, in peritonitis, and especially 

 in obstructions of the bowel. 



Indican is recognized as follows : Equal volumes of strong hydro- 

 chloric (or nitric) acid and urine are mixed in a test-tube, and, drop 

 by drop, while shaking the tube, a freshly-prepared 1 per cent, solu- 

 tion of bleaching powder is added. Normal urine shows a green 

 color only, while large quantities of indican are indicated by a more 

 or less distinct blue color. By shaking the contents of the test-tube 

 with a little chloroform, indican is dissolved by the latter, imparting 

 to it a blue color. 



Indigo-red appears in the urine in the same conditions in which 

 indican is found. It is recognized by Rosenbach's reaction : Urine 

 is boiled, and while it is still boiling nitric acid is added drop by 



