/. . /■; I 'UL OSE—LA CTOSE. 6 1 1 
(infra), while the latter La never present in the urine in amounts large 
enough to lead to confusion with glycosuria in the pathological sense; 
except when quite special substances have been taken by the mouth. But 
in order to make the identification of glucose more certain, we may confirm 
the results of a reduction test by means of yeast fermentation. Lactose and 
glycuronic acid do not ferment. The urine should be placed in a test-tube 
so as completely to lill it, and the tube inverted over a basin containing a 
further quantity of the urine. After ascertaining that no air is present, a 
small piece of pressed yeast is passed under the inverted tube, and the latter 
secured in position with a clamp. The tube is then allowed to stand at a 
temperature of 25° to 30' C. In twelve hours, if dextrose be present in 
quantity, a notable amount of carbon dioxide will have collected in the upper 
part of the tube. The fermentation test is very conclusive, but it is not easily 
obtained when less than 0*5 per cent, dextrose is present. "With phenyl- 
hydrazine, however, as already stated, urines containing as little as 0T per 
cent, will yield easily recognisable crystals of phenylglucosazone. The fact 
that laevulose also ferments with yeast, and yields an identical glucosazone, is 
of little importance in practice ; this sugar is rarely present (infra), and except 
under special circumstances it is unnecessary to distinguish it from dextrose. 
For the estimation of dextrose, modifications of the various tests just 
described are employed. We may ascertain, for instance, how much of a 
given specimen of urine is required to precipitate all the copper from a 
measured quantity of standardised Fehling solution. Or, with greater con- 
venience, we may employ the modified copper test known as Pavy's solution. 
This contains a large excess of ammonia, in addition to the ordinary constitu- 
ents of Fehling's ' test. In ammoniacal solution cupric salts are blue, but 
cuprous salts are colourless. By noting, therefore, the amount of the urine 
(diluted, if necessary, to a known bulk) which is necessary to decolorise a 
given quantity of the standard Pavy's test, we obtain a measure of its reducing 
power, and so of the dextrose present. Again, we can adapt the fermentation 
test to quantitative purposes, by measuring the CO._, produced from a definite 
quantity of the urine, or by ascertaining the diminution in the specific gravity 
of the fluid which follows the destruction of the sugar by the yeast. Lastly, 
we may employ the polarimeter, which indicates the percentage of dextrose by 
the number of degrees through which a polarised ray is turned to the right 
on passing through a layer of urine of determinate depth. A drawback to 
the use of this instrument, when applied to the urine, arises from the fact 
that other substances may be present which are optically active. 1 
(b) Laevulose. — The occurrence of laevulose in normal urine has not 
been observed ; but in certain cases of glycosuria it is said to be present. 
Kulz 2 separated from the urine of a diabetic a laworotatory sugar, 
which possessed all the properties of ordinary laevulose, except that, 
unlike the latter, it was precipitated by basic acetate of lead. When 
laevulose is given by the mouth in diabetes, it can be utilised in 
metabolism more readily than dextrose, and within certain limits of 
administration it is not excreted in the urine. Beyond these limits, 
however, it is eliminated partly unaltered and partly as dextrose. 3 
(c) Lactose. — That a reducing substance is apt to appear in the urine 
of women during the period of lactation, was first observed by Heller as 
far back as 1849; and F. Hofmeister, 4 in 1877, showed definitely that 
1 Details of all these processes will be found in practical handbooks. 
- Ztschr. f. Biol., Munchen, 1890, Bd. ix. S. 228. References to the earlier literature 
will be found in this paper. 
3 Cf. Haycraft, Ztschr. f. physiol. Chem., Strassburg, Bd. xix. S. 137; Hale White, 
Guy's Hosp. Rep., London, 1893,' p. 133. 
4 Ztschr. f. physiol. CJiem., Strassburg, 1877, Bd. i. S. 104. 
