THE AROMATIC OXY-ACIDS. 261 



(OH) 2 



Q.H. 



^H 2 .COOH dioxyphenyl-acetic acid. 



!H(OH).COOH para-oxyphenyl-glycolic acid. 



As has been pointed out, the two aromatic oxy-acids which are 

 usually found in the urine originate in the intestinal tract during 

 the process of albuminous putrefaction. There is reason to believe, 

 moreover, that homogentisinic acid and uroleucinic acid are likewise 

 of intestinal origin, and are referable to the activity of a special 

 micro-organism, which is usually not found. But as para-oxy- 

 phenyl-glycolic acid manifestly originates in the tissues of the body, 

 we must admit that the other members of the group may also be 

 formed beyond the intestinal tract. To what extent this occurs, 

 however, we do not know. 



A certain fraction of these bodies appears in the urine in com- 

 bination with sulphuric acid, but the greater portion is eliminated 

 as such, viz., as potassium and sodium salts. The amount of the 

 common oxy-acids, however, is always small, and rarely exceeds 0.03 

 gramme in the twenty-four hours. 



To demonstrate the presence of the common oxy-acids in the 

 urine, we proceed as follows : 500 c.c. of urine are strongly acidified 

 with hydrochloric acid and distilled until the phenols, viz., phenol 

 and paracresol, have passed over. This can be recognized by test- 

 ing the distillate from time to time with Millon's reagent. On 

 cooling, the remaining fluid is thoroughly extracted with ether, 

 which takes up the oxy-acids as well as pyrocatechin and hydro- 

 quinon. To separate the acids from the latter, the ethereal extract 

 is shaken with a dilute solution of sodium carbonate. The acids are 

 thus transformed into the corresponding salts and are found in the 

 alkaline solution. After separation from the ether this is acidified 

 with dilute sulphuric acid and extracted with ether. The ethereal 

 solution contains the free oxy-acids. Their presence can be demon- 

 strated by evaporating to dry ness, when the residue is dissolved in a 

 little water and tested with Millon's reagent. 



To isolate the individual acids, much larger quantities of urine 

 are necessary. We may then proceed as described in the section on 

 the Feces. 



Homogentisinic Acid. The presence of homogentisinic acid 

 may be suspected if a urine, on being rendered alkaline, turns a 

 dark reddish-brown on standing, and ultimately becomes black. At 

 the same time a positive reaction with Fehling's solution is obtained, 

 while polarimetric examination shows that the urine is optically 

 inactive. Ny lander's solution is not reduced. Upon the addition 

 of a small amount of a dilute solution of ferric chloride a greenish- 

 blue color develops, which is only of momentary occurrence, how- 

 ever. 



