298 THE URINE. 



DIFFERENTIAL DENSITY METHOD. The specific gravity is first 

 determined in the fresh urine, after adding 2 grammes of tartrate 

 of potassium and sodium, and 2 grammes of diacid sodium phos- 

 phate to every 100 c.c. To about 200 c.c. which have thus been 

 prepared, from 5 to 10 grammes of fresh yeast are added, and the 

 mixture is set aside at a temperature of from 20 to 25 C. until 

 fermentation is completed. If but little sugar is present, two or 

 three hours will suffice; otherwise the mixture is allowed to stand 

 for twelve hours. Evaporation is guarded against by closing the 

 bottle with a perforated stopper through which a finely drawn out 

 tube passes, which is open at the distal end. The specific gravity is 

 then again determined at the same time as before, and the difference 

 multiplied by 0.230. The result indicates the amount of sugar in 

 per cent. 



The method yields good results unless very small amounts of 

 sugar are present, viz., less than 0.5 per cent. In such an event, 

 the reducing power of the urine is first ascertained according to 

 Fehling's or Knapp's method. It is then fermented, when the 

 remaining reducing substances are again determined. The differ- 

 ence may be referred to sugar. 



FERMENTATION METHOD. In the clinical laboratory especially 

 constructed saccharimetric tubes are used, of which Lohnstein's is 

 probably the best. These are provided with a scale which enables 

 the percentage of sugar to be read off directly from the amount of 

 carbonic acid that has gathered in the upper end of the tube. The 

 instruments are accompanied by printed instructions, which need 

 not be considered at this place. 



Lactose. The presence of lactose in the urine is a normal 

 occurrence in nursing women, and it is at times found also shortly 

 before confinement. Its appearance in the urine is undoubtedly 

 referable to absorption, owing to the fact that a superabundance of 

 milk is being produced, and we accordingly also find the substance 

 in the urine when for any reason lactation is suppressed. Once it 

 has found its way into the circulation, its elimination through the 

 kidneys necessarily follows, as the body is incapable of inverting 

 the disaccharides to monosaccharides. 



Aside from its occurrence in connection with lactation, lactose 

 is found in the urine only if abnormally large amounts have been 

 ingested. In such an event, as has been stated, a certain proportion 

 of the sugar escapes inversion, and on entering the general circula- 

 tion it is eliminated as such. The amount of lactose which may be 

 found in the urine of nursing women varies between 0.013 and 

 0.438 per cent. Its presence in the urine may be suspected if the 

 reduction test and the phenylhydrazin test yield a positive result, 

 while the fermentation test, as usually conducted, is negative. Like 

 glucose, the substance is dextrorotatory. To identify the sugar 

 positively as lactose, it is necessary to isolate it as such. 



