274 PKACTICAL PHYSIOLOGY 



The percentage of these bodies in normal urine is, however, too low to 

 cause the reduction, and it is only where a concentrated urine is employed 

 that there is any chance of confusion. If the tests are applied as above 

 described, the chance of error is very much lessened. There are, how- 

 ever, certain tests which are given only by dextrose, and these are : 



1. The Fermentation Test. EXPERIMENT VII. Place some diabetic 

 urine in a small beaker, and boil it on a sand bath for ten minutes 

 (this expels any air it may contain). Cool the urine and test its 

 reaction; if alkaline, render faintly acid with a weak solution of 

 tartaric acid. (This precaution is necessary in order to prevent putre- 

 faction, which would lead to the, evolution of ammonia. ) Add a small 

 piece (about the size of a split pea) of German yeast, and stir it in 

 the urine until a milky solution is obtained. Now transfer the fluid 

 to a Doremus ureometer (Fig. 164) so that the upright limb is com- 

 pletely filled with fluid. Place this in an incubator, 

 or in a warm place, as on the mantelpiece, over 

 night when it will be found that gas C0 2 has 

 collected in the upper portion of the vertical limb. 1 

 Two control tubes one with a weak solution of 

 dextrose and yeast, the other with normal urine and 

 yeast should be arranged so as to prevent any 

 fallacy due to inactive or impure yeast 



Instead of using a Doremus' ureometer a test-tube 

 inverted in a trough of mercury may be employed. 



2. The Phenyl Hydrazine Test. The method of 

 employing this is described in the Advanced Course 

 (see p. 417). 



Quantitative Determination of Sugar. Two re- 

 Fia7i64. Ureo- actions of sugar are taken advantage of in order 

 to estimate the amount of it present in any solution. 

 The one depends on its reducing power, and the other on its power of 

 rotating polarized light. In this country it is usually the former of 

 these which is employed, so that it is the only method which we will 

 describe here. The principle and technique of the polarimetric method 

 is described on p. 421. 



To determine the reducing power of any fluid, the latter, diluted if 

 necessary, is run from a burette into a measured quantity of boiling 

 Fehling's solution, which is made of such a strength that 10 c.c. cor- 

 respond to 0'05 grammes of dextrose. When all the blue colour of the 

 Fehling's solution has been discharged, the number of c.c. of fluid 

 required is read off, and the percentage calculated (Fig. 165). 



1 Tubes, similar in construction to Doremus' ureometer, are prepared in which 

 the vertical limb is graduated in percentages of dextrose. 



