Licence: Public Domain Mark
Credit: The diseases of the stomach / by Dr. C.A. Ewald. Source: Wellcome Collection.
Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.
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![from them by fermentation. So far as we know, tlie only one which is not so formed is sarcolactic acid, which is dissolved from meat in which it is always present. Tests for Lactic Acid.—There are two kinds of lactic acid : fer- tnentation lactic acid and sarcolactic acid. They are distinguished not so much by differences in chemical character as by their source. The former is of more importance to us than the latter, yet the tests to be described presently apply to both kinds. The method used by chemists to determine the presence of lactic acid is a very elaborate one, and is too complicated for general use. A very sim- ple and rapid test for medical practice has been proposed by Uffel- mann. Diluted solutions of neutral ferric chloride turn canary yellow or greenish yellow in the presence of lactic acid.* If some ferric chloride solution is diluted till it is almost colorless, and a trace of lactic acid is added, a canary-yellow color will at once appear. Nevertheless, the reaction is somewhat uncertain, or rather difficult of recognition, because we must merely distinguish the intensity of otherwise similar shades of color. Hence the test was modified by adding one or two drops of pure carbolic acid to the above solution; or a few c. c. of a dilute carbolic acid solution, say 10 c. c. [3 ijss.] of a 2 to 5 per cent solution of carboKc acid—^the exact proportions are not essential—are mixed with one or two drops of ferric chloride solution and diluted with water till the solution assumes a beautiful amethyst-blue color. The addition of lactic acid changes the color to the same canary or greenish yellow described above, and a good con- trast is thus obtained. A few drops of even a 0*05 per thousand solu- tion of lactic acid [1 in 20,000] will suffice to change this blue to the characteristic yellow color. The delicacy of the reaction is such that 2 c. c. [3 ss.] of this Uffelmann's reagent will give a distinct re- sult on adding 0*8 c. c. [12 minims] of a lactic acid solution of 0*01 per cent; with 0*6 c. c. [9 minims] of the same solution the color is pale yellow; but no yellow color is recognizable on adding only 0*3 c. c. [4r^ minims]. The reagent soon decolorizes, and hence must be * [All recent writers lay great stress upon the greenish color of the reaction; when in doubt as to the exact color it is wise to add a drop of lactic acid to a small quantity of UflFelmann's reagent in a test tube and to use this as a standard for comparison.—Ed.]](https://iiif.wellcomecollection.org/image/b21223026_0055.jp2/full/800%2C/0/default.jpg)
