262 THE URINE. 



Boedeker was the first to describe a urine of this kind, and termed 

 the substance giving rise to the above reaction alkapton. Subse- 

 quently, however, he expressed the opinion that his alkapton may 

 have been pyrocatechin. Other investigators have isolated sub- 

 stances from such urines, which have been variously termed pyro- 

 catechuic acid, urrhodinic acid, glycosuric acid, uroxanthinic acid, 

 and uroleucinic acid, but there is reason to suppose that, with the 

 possible exception of the last mentioned, all these substances are 

 identical with homogentisinic acid. This was first isolated from an 

 " alkapton " urine by Baumann and Wolkow, and has since been 

 found in every case that has been examined in this direction. 



Alkaptonuria, though it may occur in disease, is generally regarded 

 as the expression of an unusual form of intestinal putrefaction 

 which in no way affects the health of the individual. Some ob- 

 servers, on the other hand, look upon it as a metabolic abnormality, 

 and it must be confessed that micro-organisms have thus far not 

 been isolated from the intestinal contents of such cases which are 

 capable of effecting the transformation of tyrosin to homogentisinic 

 acid in vitro. That tyrosin, indeed, is its ultimate source cannot be 

 doubted, and it has been shown, as a matter of fact, that following 

 the administration of this substance homogentisinic acid appears in 

 the urine in greatly increased amount. Baumann thus noted that 

 while the average elimination in one of his cases amounted to 4.6 

 grammes, 14 grammes were once extracted in the twenty-four hours 

 after tyrosin had been ingested. 



Isolation. Homogentisinic acid may be conveniently isolated 

 from the urine according to the method suggested by Garrod. The 

 collected urine of twenty-four hours is heated nearly to the boiling- 

 point, and then treated with 5 or 6 grammes of neutral lead acetate 

 in substance for every 100 c.c. of the urine. As soon as the salt is 

 dissolved, the resulting precipitate is filtered off and the filtrate set 

 aside in the cold for twenty-four hours. The crystals of lead homo- 

 gentisinate are then collected on a filter and dissolved in hot water. 

 This solution gives the various reactions described above. To isolate 

 the free acid, the lead compound is decomposed with hydrogen sul- 

 phide and the filtrate carefully evaporated on a water-bath until the 

 fluid begins to darken, when it is further concentrated in a vacuum 

 to the point of crystallization. The resulting crystals are soluble in 

 water, alcohol, and ether, but are insoluble in chloroform, benzol, 

 and toluol. They melt at 146.5-147 C. 



Uroleucinic acid has been found only once in an alkapton urine. 

 In its general reactions it resembles homogentisinic acid, but does not 

 give the iron reaction described above. Unlike the latter, it reduces 

 Nylander's solution when present to the extent of 0.5 per cent, or 

 more. 



Inosit. The origin and chemical constitution of inosit will be 

 considered elsewhere. According to Hoppe-Seyler, it may occur in 

 the urine under normal conditions, but more commonly it is found 



