472 PHYSIOLOGICAL CHEMISTRY. 



imparting to it a gray color ; the test should then be repeated with a 

 smaller amount of the bismuth salt. (Plate VIII., 6.) 



The above test may be somewhat modified by using a bismuth 

 solution, instead of the powder. The solution known as Nylander's 

 reagent is made by dissolving 2 grammes of bismuth subnitrate, 4 

 grammes of Rochelle salt, and 10 grammes of sodium hydroxide in 

 90 c.c. of water, and filtering. One-half c c. of this solution is heated 

 with about 5 c.c. of urine, when, in the presence of sugar, a brown or 

 black precipitate will form after a few minutes. 



If the urine contains hydrogen disulphide (sometimes produced by decom- 

 position of certain urinary constituents), black bismuth sulphide will be 

 formed, which may be mistaken for metallic bismuth ; albumin itself may be 

 the cause of the formation of alkaline sulphides : the previous complete separa- 

 tion of albumin is therefore indispensable. 



Moore's or Seller's test is made by heating urine with about one- 

 fourth of its volume of solution of potassium hydroxide. In the 

 presence of sugar the color of the mixture will deepen to a dark 

 yellow or brown, and the depth of color is a fair indication of the 

 quantity of sugar present. In case but a slight change takes place 

 in color, it is well to compare it with that of an unchanged specimen 

 of the urine. 



The fermentation test is based upon the decomposition of sugar by 

 the action of yeast with generation of carbon dioxide. The test is 

 made by adding to about 50 or 100 c.c. of urine (contained in a large 

 test-tube or small flask) a few grammes of common yeast. The vessel 

 containing the urine is provided with a perforated cork, through 

 which is passed one limb of a bent glass tube, long enough to reach 

 nearly to the bottom of the vessel, which should be completely filled 

 with urine. Under the second limb of the bent glass tube is placed 

 a beaker. 



The apparatus thus prepared is placed in a room having a tem- 

 perature of about 22-28 C. (72-82 F.). If sugar be present, fer- 

 mentation will commence within twelve hours, and will manifest 

 itself by the formation of carbon dioxide, which will force a portion 

 of the fluid through the bent tube into the beaker placed there for 

 its reception. 



The disadvantages of this process are the length of time required for its per- 

 formance, the unreliability of the ferment, and the fact that small quantities of 

 sugar (less than 0.5 per cent.) evolve so little carbon dioxide that a doubt may 

 be felt as to the presence of sugar at all. 



