It frequently happens that the sugar is present in such quantities that we are able to observe its power to rotate the plane of polarized light.
For this purpose we generally use Soleil-Ventzke’s penumbra-polarization apparatus, a description of which will be found in the hand-books on the subject.
This apparatus suffices to investigate the dextro-rotatory and lævo-rotatory substances in the urine. With its assistance it is also possible to determine the quantity of sugar in the urine. In addition for the determination of the quantity of sugar in the urine a number of chemical processes can be employed, such, for instance, as Fehling’s method with Worm-Müller’s modification, Knapp’s method, and various others.
If we add to normal urine a dilute solution of potassium permanganate it at once loses its color. From this we perceive that the urine contains a great quantity of oxidizable or so-called reducing substances.
It has been already mentioned that Trommer’s test gives positive results after protracted boiling, even in the case of normal urine, without any corresponding quantity of grape-sugar being present. In this case the reducing substances interfere with the test in consequence of their tendency to become oxidized.
We find a number of them in the urine. Foremost among them are uric acid, creatinine, and the coloring-matter. Also the substances mentioned above in the description of the carbo-hydrates have reducing properties.
Different statements have been made as to the quantity of reducing substances existing in the urine. According to Flückiger they form from 0.15 to 0.25 per cent.; according to Salkowski an average of 0.4 per cent., and according to Munk an average of 0.3 per cent.
Moritz found the quantity of reducing substances range between 2.93 and 4.1 grammes per diem in a grown man. His investigations were made with the collected urine of 24 hours, and were applied to that of men, women, and children. The result showed that men always excreted a greater quantity of reducing substances than women of the same age who used the same food.