282 THE URINE. 



thi' bottom and the supernatant fluid becomes clear. The final point 

 is reached when a drop of the liquid, placed upon filter-paper, and 

 successively held over the rnouth of a bottle containing fuming 

 hydrochloric acid and over that of one containing a strong solution 

 of hydrogen sulphide, is no longer colored yellow. The results arc 

 then calculated on the basis outlined above. 



FEHLING'S METHOD. For a consideration of this method, which 

 at best is open to numerous objections, and which sometimes leads to 

 no end whatever, the reader is referred to other works. At this 

 place it may well be omitted. 



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

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

 diately preceding confinement. Its appearance in the urine is un- 

 doubtedly referable to absorption, owing to the fact that a super- 

 abundance of milk is being produced, and we accordingly also find 

 the substance in the urine when for any reason lactation is sup- 

 pressed. Once it has found its way into the circulation, its elimina- 

 tion 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 in the epithelial cells which line the 

 intestinal tract, and on entering the general circulation it is elimi- 

 nated 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 fermenta- 

 tion test, as usually conducted, is negative. Like glucose, the sub- 

 stance is dextrorotatory. To identify the sugar positively as lactose, 

 however, it is necessary to isolate it as such. 



Isolation. The collected urine of twenty-four hours is precipi- 

 tated with lead subacetate and filtered. After washing with watc r 

 the filtrate and washings are mixed and treated with ammonia. 

 The resulting precipitate is filtered off and the filtrate again pre- 

 cipitated with lead subacetate and ammonia, and so on until the 

 final filtrate is optically inactive. The precipitates, with the excep- 

 tion of the first, are then mixed, washed with water, decomposed 

 with hydrogen sulphide, and filtered. In the filtrate the excess of 

 hydrogen sulphide is removed by a current of air, and freed from 

 any acids that have been liberated by shaking with argentic oxide. 

 The mixture is filtered, freed from soluble silver with hydrogen sul- 

 phide, treated with barium carbonate, and concentrated to a small 

 volume ; 90 per cent, alcohol is then added, which causes the 

 formation of a flocculent precipitate. This is filtered off. The 

 filtrate is placed in the desiccator, when on standing crystals of 

 lactose gradually separate out. These may be purified by recrys- 



