L^E VUL OSE LA CTOSE. 6 1 1 



(infra), while the latter is 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 fill 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 O'l per 

 cent, will yield easily recognisable crystals of phenylglucosazone. The fact 

 that Isevulose 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 C0 2 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 laevorotatory 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. 



2 Ztschr.f. BioL, Miinchen, 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. 



14 Ztschr. /. physiol. Chem., Strassburg, 1877, Bd. i. S. 104. 



