284 THE URINE. 



of the pentoses which are found in the urine. As a general rule, 

 it is true, ingested pentoses are mostly decomposed within the body; 

 but in chickens and rabbits, in which a more marked ability exists 

 to effect their oxidation than in man, this is never complete. As in 

 the case of glucose, the power to assimilate pentoses seems to vary 

 with different individuals, and here, as there, a digestive pentosuria 

 can artificially be produced. In diabetes also the power to oxidize 

 the pentoses may be much impaired, and, very curiously, the largest 

 quantities have thus far been observed in morphin habitiite. 



The individual pentoses which have thus far been encountered in 

 the urine are arabinose, xylose, and rhamnose. They all reduce 

 Fehling's solution, and give rise to osazons with phenylhydrazin. 

 The melting-points of the resulting compounds, however, are differ- 

 ent from those of the common hexosazons (see page 280). In the 

 amounts, however, in which they are usually present no reactions 

 are obtained in this manner. The fermentation test is not obtained. 

 Xylose and rhamnose turn the plane of polarization to the right, 

 while arabinose is optically inactive. 



To demonstrate the presence of pentoses in the urine the following 

 test of Tollens is employed : 



A saturated solution of orcin in concentrated hydrochloric acid is 

 first prepared, and should contain a slight excess of the substance. 

 Six c.c. of this are divided into two equal parts and are allowed to 

 cool. To one portion 0.5 c.c. of the urine under examination is 

 added, while the other is treated with the same amount of normal 

 urine of a like specific gravity. In either case it is well first to 

 decolorize the urine with animal charcoal. Both specimens are 

 then placed in a beaker with boiling water, when the urine contain- 

 ing pentoses gradually assumes a green color, which begins in the 

 surface layers, while the color of the normal urine is scarcely changed. 

 One-tenth per cent, of pentoses can thus be demonstrated. 



AVith Tollens' phloroglucin test, which is conducted in the same 

 manner, a deep-red color develops instead ; but this reaction is also 

 common to the glucuronates. (The reagent is prepared in the same 

 manner as in the case of the orcin reagent, phloroglucin being simply 

 substituted for the orcin.) 



THE ALBUMINS. 



As every urine contains a small number of cellular- elements 

 which are derived from the urinary tract, it can readily be under- 

 stood that even under normal conditions albumin can be demon- 

 strated with suitable methods. The amount, however, is exceed- 

 ingly small, and with the common tests a positive reaction cannot 

 be obtained unless the substance in question has been previously 

 isolated from a large quantity of urine. In such an event a trace 

 of a nucleo-albumin can be demonstrated. The occurrence of the 

 common albumins of the blood, on the other hand, is always a 



