288 PHYSIOLOGICAL CHEMISTRY. 



They are products of the putrefaction of protein material and 

 tyrosine is an intermediate stage in their formation. Both these 

 acids for the most part pass unchanged into the urine where they 

 occur normally in very small amount. The content may be in- 

 creased in the same manner as the phenol content, in particular by 

 acute phosphorus poisoning. A fraction of the total aromatic oxy- 

 acid content of the urine is in combination with sulphuric acid, but 

 the greater part is present in the form of salts of sodium and 

 potassium. 



Homogentisic Acid or di-oxyphenyl-acetic acid, 



OH 



CH 2 -COOH, 



is another important oxyacid sometimes present in the urine. 

 Under the name glycosuric acid it was first isolated from the urine 

 by Prof. John Marshall of the University of Pennsylvania; sub- 

 sequently Baumann isolated it and determined its chemical constitu- 

 tion. It occurs in cases of alcaptonuvia. A urine containing this 

 oxyacid turns greenish-brown from the surface downward when 

 treated with a little sodium hydroxide or ammonia. If the solution 

 be stirred the color very soon becomes dark brown or even black. 

 Homogentisic acid reduces alkaline copper solutions but not alka- 

 line bismuth solutions. Uroleucic acid is similar in its reactions 

 to homogentisic acid. 



Oxymandelic Acid or paraoxyphenyl-gly colic acid, 



OH 



CH(OH)-COOH, 



has been detected in the urine in cases of yellow atrophy of the 

 liver. 



Kynurenic Acid or y-oxy-/3-quinoline carbonic acid, 



CH COH 



/\/\ 

 HC C C-COOH, 



I! 



n 



\/\/ 



CH N 



