EXAMINATION OF DIABETIC URINE GRAPE SUGAR.
Several tests should always be employed in order to determine with certainty the presence of grape sugar. Some of these are very easily made and serve for a provisional diagnosis, others demand more time and may be employed to confirm this provisional diagnosis. If albumin is present in the urine, it should be removed by boiling and filtering before the test for sugar is made.
For this purpose Trommer's and Nylander's reduction tests and Moore's reagent are the most suitable.
a. Trommers' : (1) A 10-per-cent. solution of caustic soda or potash; (2) A 5-per-cent. solution of copper sulphate.
Principle : Copper sulphate when heated with glucose in an alka line solution is reduced to red oxide of copper (CIO) and yellow oxide of copper Application: 5 c.c. urine and 5 c.c. solution of caustic soda are mixed in a test-tube. Then the copper sulphate is added a drop at a time until on shaking it is no longer dissolved. If sugar 1w present the cold fluid assumes a dark-blue color, and when heated, even before the boiling-point is reached, an orange-red precipitate is formed. If on heating and boiling the fluid is only colored yellow without any orange-red precipitate, or if the yellow precipitate is thrown down only on cooling, the presence of sugar may be suspected but is not actually proven; for usually then the yellow coloration of the fluid and the precipitation of copper oxide are due to the presence of other reducing substances.
In urine which contains few other organic substances than sugar, the test will show 0.2 to 0.3 per cent. of sugar; but when there is an abundance of uric acid, creatiniu, and other amido-combinations, or of free ammonia, the test will show with certainty not less than 1 per cent. The delicacy of the reaction is increased if the urine is previously filtered through animal charcoal.
Partly on account of its want of delicacy and partly because of a certain capriciousness, the reasons for which are not always very evi dent, this reaction does not really deserve the popularity which it enjoys. After having compared Trommer's and Nylander's tests in every case of saccharine which I have examined for many years, I have come to the conclusion that the latter is by far preferable.
b. Xylander's Test.—Reagents : 4 gm. sodium tartrate are dis solved in 100 c.c. of a 10-per-cent. solution of caustic soda, to which 2 gm. subnitrate of bismuth are added. The mixture is heated up to 50° C. (122° F.), and filtered when cool. The reagent may be kept unaltered for months.
Principle : Subnitrate of bismuth in contact with grape sugar in a boiling alkaline solution is reduced to black metallic bismuth.
Application: 10 c.c. of urine and 1 c.c. of the reagent are boiled for two minutes. If sugar be present there is a brown to black colora tion of the fluid or precipitate, metallic bismuth being thrown down. If the dark coloration takes place gradually as the fluid cools, the presence of sugar is not proven. The reaction takes place when sugar is present in the proportion of 0.1 per cent. But as other sub stances (in particular medicinal and vegetable substances which are excreted in the urine) give rise to the same reaction, we cannot be sure when it is obtained that sugar is always present. The absence of a reaction is, however, positive proof that sugar is not present in the above-mentioned proportion.
c. Hoore's Test.-3 c.c. of a 10-per-cent. solution of caustic potash and 10 c.c. of the suspected urine are thoroughly mixed together. The upper portion of the fluid is then heated and boiled for at least one minute. If sugar be present in the proportion of at least 0.5 per cent. the heated layer becomes of a brown color which grows darker with further heating. Normal urine shows under the same conditions only a dark-yellow coloration.
The tests above described are only provisional, as the reaction may be caused by the presence of other substances than sugar. If all three tests, especially Nylander's, give a negative result then any further test is unnecessary. If they all give positive results the pres ence of sugar is at least very probable. Nevertheless it is better to have the evidence of other tests. This is absolutely necessary when the provisional tests have given uncertain or contradictory results.