6o8 THE CHEMISTR Y OF THE URINE. 
The general chemistry of the carbohydrates is elsewhere discussed. 
We shall deal i inly with their relation to the urine : — 
(a) Dextrose. — The question as to whether or not small amounts of 
grape-sugar are excreted in the urine during normal health has been 
much debated. It is needless to confuse the issue by an attempt to 
define what is meant by " normal " urine. We may ask rather, Does 
the urine of the average individual, living an ordinary life, upon ordi- 
nary diet, generally contain sugar ? There can lie little doubt, in the 
light of our present knowledge, that this question must be answered in 
the affirmative. 
Briicke 1 was the first (in 1858) to state that sugar is normally present in 
human urine, and Bence Jones 2 was an early supporter of the view. For 
some years, however, the question was treated as an open one, and in 1871, 
Seegen, after careful study of the matter, decided that means were not then 
to hand by which its presence could he proved with certainty. Pavy, 3 in 
1878, affirmed that it was certainly a normal constituent, and has always 
maintained this position. Since then other observers (in England especially 
Sir G. Johnson and G. Stillingfleet Johnson 4 ) have stoutly maintained the 
contrary. The chief criticism of the earlier methods of demonstration which 
gave positive results was that, while they depended upon reduction tests, they 
did not eliminate the influence of other reducing substances. The creatinin, 
uric acid, hippuric acid, and other aromatic constituents of the urine, all tend 
to reduce salts of the heavy metals in alkaline solution. It is admitted by all 
observers that normal urine exercises a reducing power on copper solutions, 
which, if due to glucose, would indicate the presence of about OT to - 3 per 
cent, of this substance. But it is equally admitted by all that a large part of 
this reduction is due to the other substances mentioned above. The question 
which has been at issue is as to whether any part of the reducing power is due 
to sugar. 
It is evident that we cannot rely alone upon reduction tests applied to 
the original urine. The more accurate knowledge that we now posesss with 
regard to the question has been obtained by three lines of investigation: — 
(1) By the application of direct tests which are unaffected by substances 
other than sugar; (2) by the use of methods which involve a preliminary 
removal of interfering substances ; and (3) by the employment of means 
whereby the sugar itself is separated from the urine unmixed with the con- 
stituents which lead to error. 
1. The phenylhydrazine test of Fischer and r. Jaksch has given positive 
results in the hands of several observers when applied directly to normal urine. 5 
The yellow crystals of phenylglucosazone may certainly be obtained from 
urine containing as little as OT per cent, of sugar (v. Jaksch). In my own 
experience great care is generally necessary to secure unequivocal results in the 
case of normal urine. As a crucial test, it suffers the disadvantage of yielding 
crystals with the glycuronic acid compounds; the amount of crystals obtain- 
able from normal urine direct being in general too small for discriminating 
tests to l>e applied to them. After the sugar has been previously isolated, the 
reaction with phenylhydrazine is, however, of the utmost value as a confirma- 
tory test {vide infra). 
A colour reaction may be observed in normal urine, which is held by some 
to be conclusive of the presence of sugar. This is the furfurol reaction. A 
1 Sitzungsh. rf. 1c. Akad. d. Wisscnsch., Wien, 185S, Bd. xxix. S. 346. 
2 Journ. Chem. Soc, London, vol. xiv. p. 22. 
3 Gwy's Hosp. Rep., London, vol. xxi. p. 413. 
4 See articles and correspondence in the Lancet, London, during July and August 1894. 
5 Cf. E. Roos, Ztschr.f. physiol. Chan., Strassburg, 1891, Bd. xv. S. 523 ; A. H. Allen, 
"Chemistry of the Urine," 1895, p. 89. 
