608 THE CHEMISTR Y OF THE URINE. 



The general chemistry of the carbohydrates is elsewhere discussed. 

 We shall deal only 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 be little doubt, in the 

 light of our present knowledge, that this question must be answered in 

 the affirmative. 



Briicke l was the first (in 1858) to state that sugar is normally present in 

 human urine, and Bence Jones 2 was a^ 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 be 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 O'l to 0*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 plienylhydrazine test of Fischer and v. Jakscli 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 O'l per cent, of sugar (v. Jakscli). 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 be 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 furfural reaction. A 



1 Sitzungsb. d. Jc. Akad. d. Wissensch., Wien, 1858, Bd. xxix. S. 346. 



2 Journ. Chem. Soc. , London, vol. xiv. p. 22. 



3 Guy's Hosp. Rep., London, vol. x'xi. p. 413. 



4 See articles and correspondence in the Lancet, London, during July and August 1894. 



5 Cf. E. Roos, Ztschr.f. physiol. Chem., Strassburg, 1891, Bd. xv. S. 523; A. H. Allen, 

 " Chemistry of the Urine," 1895, p. 89. 



