294 THE URINE. 



in the proportion of 11:1, and boiled, when in the presence of 

 sugar a reduction of the subnitrate of bismuth to bismuthous oxide, 

 or even to the metallic form, occurs. As a consequence the mixture 

 assumes a grayish, dark-brown, or black color, and on standing the 

 precipitated oxide or metal settles to the bottom together with the 

 earthy phosphates. 



FEHLING'S TEST. This is merely a modification of the older 

 Trommer's test. The reagent consists of two solutions, viz., one 

 containing 34.64 grammes of copper sulphate in 500 c.c. of water, 

 while the other is prepared by dissolving 173 grammes of tartrate 

 of potassium and sodium and 125 grammes of caustic soda in a like 

 amount of water. Before using, equal parts of the two solutions 

 are mixed and diluted with four times as much water. A few cubic 

 centimeters of the resulting reagent are boiled and treated with a 

 small amount of the urine, when in the presence of sugar yellow 

 cuprous hydroxide or red cuprous oxide separates out, and on stand- 

 ing settles to the bottom. After the addition of the urine the solu- 

 tions should no longer be boiled, but may be held near the flame 

 for a few moments. Unless this precaution is taken, fallacious 

 results are often obtained, as uric acid, and kreatinin more especially, 

 may cause a partial reduction of the copper solution on prolonged 

 boiling. Conjugate glucuronates and homogentisinic acid likewise 

 give a positive reaction, and ammonia, if present beyond traces, 

 may hold in solution any cuprous oxide that may be referable to 

 very small amounts of sugar. 



FERMENTATION TEST. This test, when controlled by Nylander's 

 test, is the most satisfactory one. To this end, a little compressed 

 yeast is shaken with about 20 c.c. of urine, and the mixture is 

 placed in a saccharimetric tube, such as that devised by Lohnstein 

 or Einhorn. On standing at the ordinary temperature of the room, 

 or, still better, at 37 C., fermentation occurs if glucose is present, 

 and the liberated carbon dioxide collects at the top of the tube. 

 In any case, however, two controls should be made, viz., one to 

 determine that the yeast is active, and another with normal urine. 

 If a small amount of sugar is present, it may happen that the 

 resulting carbon dioxide is absorbed. If in such a case Nylander's 

 test first gave a positive reaction, but no longer reacts after fermenta- 

 tion is complete (in twelve to twenty-four hours), the presence of 

 sugar may be inferred. If, on the other hand, no fermentation 

 occurs, and Nylander's test still gives a positive result, we may con- 

 clude that the reaction is due to the presence of a non-fermentable 

 reducing substance. 



PHENYLHYDRAZIN TEST. As has been pointed out, all mono- 

 saccharides and some of the disaccharides, such as maltose, isomal- 

 tose, and lactose, form compounds with phenylhydrazin which are 

 known as osazons (see page 65). The resulting bodies are all very 

 similar, but may be distinguished from each other by the melting- 

 point of their crystals, and to some extent also by their microscopical 



