But our attention must be directed, not to the sugar alone, but to a number of other so-called reducing substances, because these, as regards certain reactions, resemble grape-sugar, and have to be distinguished from it.
In the year 1858 my highly-revered master, E. Brücke, drew attention to the presence of grape-sugar in normal urine. The foundation of the theory of normal glycosuria was laid by his obtaining the potassium compound of sugar (zuckerkali) from large quantities of urine. His theory has been since much elaborated, and a great deal written both for and against it. When this symptom in the urine reaches a certain proportion per cent., the condition of the individual must be described as diseased.
If we apply qualitative chemical tests for sugar, we soon find that they are disturbed by a number of reducing substances which exist in the urine, and it is often difficult to determine whether the processes used to discover the sugar do not produce more reducing substances than the sugar itself.
Bence-Jones agrees with Brücke’s opinion respecting the presence of sugar in normal urine, and insists upon its power to rotate the plane of polarization to the right. More recent authors, Ivanof, Huizinga, Pavy, Abeles, have stated this fact in different ways, and it yet remains to be verified. The fact existed, but not without meeting with contradiction. Maly, Seegen, Friedländer, and many others sought to oppose the view.
Although in many cases with the commonly used reactions it is impossible to demonstrate the presence of sugar in samples of urine, nevertheless, the sugar has been isolated in considerable quantities, by means of precipitation with acetate of lead and ammonia, and by subsequent decomposition of the precipitate with sulphuretted hydrogen (E. Ludwig), after which it has been successfully tested and recognized by characteristic reactions.
We shall here concern ourselves principally with the appearance or the increase of the sugar, so far as its presence according to the views hitherto held is normal.
We are acquainted with a so-called alimentary glycosuria, which is occasioned by this, that the individual in question, after having eaten an excessive quantity of sugar, easily recognizes an increase of the quantity of sugar in the urine. But there are also individuals, who, though they may have eaten a very large quantity of sugar, cannot afterwards discover a trace of it in the urine. In these cases complete combustion has taken place.
But here we must also next direct our attention to the fact that there are persons who, in the digestion of their food under all circumstances, excrete sugar, though perhaps in very small quantities. Others, after eating proportionately much larger quantities, excrete no perceptible sugar in the urine. Hoppe-Seyler, after having eaten 225 grammes of sugar, could find no trace of it in his urine. (Moritz.) Frerichs admits exceptions, and relates that in the case of two men he could always discover sugar in the urine after they had eaten sugar, although he considered both healthy. Then we find specialists like Budge, C. Schmidt, Mosler, Schiff, Vogel, C. Ludwig, Voit, etc., who admit, after their experiments with men and beasts, an artificial glycosuria, which is normal. Seegen, after feeding dogs with cane sugar, found inverted sugar (invertzucker) in the urine. The sugar which he was able to identify was of two kinds, one of them turning the polarization plane to the right, and the other turning it to the left.