But while Johnson claims that neither coloring matters of normal urine nor uric acid reduce the picric acid, he admits that he has tested with picric acid and potash a large number of specimens of normal urine with the almost uniform result of a depth of color indicating the proportion of .6 of a grain of sugar to the fluidounce, the indication varying between the limits of .5 to .7 grain. The ammonio-cupric method used at the same time gave results of from .7 to .9 grain to the fluidounce, or an excess of .1 to .3 grain. Now, if my own views, the grounds for which are announced elsewhere,[43] are correct, strictly normal urine contains no sugar, and any reducing action upon oxide of copper is due to uric acid, either picric acid is reduced to a degree by uric acid or by some other constituent of normal urine. This, in the light of Oliver's[44] recent investigations, may be kreatinin. For he has shown that kreatinin strikes in a few seconds a red color with the cold alkaline picric solution, which is quickened by heat. From this it would seem that the exact value of the picric-acid test has as yet to be determined. [Footnote 43: Tyson, _Practical Examination of Urine_, 4th ed., Philadelphia, 1884.] [Footnote 44: _On Bedside Urine-Testing, including Qualitative Albumen and Sugar_, by Geo. Oliver, M.D., London, Member of the Royal College of Physicians of Lond., etc., 2d ed., London, 1884.] {216} The Indigo-Carmine Test.--The fact that indigotine, the coloring matter of commercial indigo, is converted into indigo when heated with an alkali in the presence of glucose and certain carbohydrates, has recently been applied by George Oliver of London in the construction of a test-paper. Carmine of indigo is the sulph-indigotate of sodium, an intensely blue salt, soluble in 120 parts of water. Sulph-indigotic acid is made by heating indigo with sulphuric acid, and when combined with a base, sodium, produces indigo-carmine. When sodium carbonate is mixed with a solution of indigo-carmine, the latter is precipitated in a minute state of division, but is redissolved on heating, when there results a greenish-blue solution. A freshly-made mixture of the indigo solution and sodium carbonate furnishes a fluid not unlike Fehling's solution, which gives the reaction to be described with glucose. Unfortunately, such a mixture will not keep, and the reagent would be useless but for the happy idea of Oliver of making the test-paper. In doing this bibulous paper is immersed in a solution of indigo-carmine with carbonate of sodium.[45] The paper is then cut into strips an inch long and one-quarter of an inch wide.