THE AROMATIC OXY-ACIDS. 273 



The mother-liquor is then extracted with acetic ether, which takes 

 up the acid. On evaporation the residue is dissolved in a dilute 

 solution of sodium hydrate. From this solution the substance is 

 again extracted with ether, after acidifying with hydrochloric acid, 

 and thus purified, and finally allowed to crystallize from its aqueous 

 solution. 



In this connection brief reference may be made to ornithuric acid, 

 which may be obtained from the urine of birds when these are fed 

 with benzoic acid, and which probably also represents a normal con- 

 stituent of such urine. Its formation is analogous to that of hip- 

 puric acid in mammals, but the benzoic acid here combines with 

 ornithin, which is a, d-diamino-valerianic acid, as has been shown 

 before. 



The relation of ornithin to arginin has already been considered. 



' 

 THE AROMATIC OXY-ACIDS. 



The aromatic oxy-acids which may be found in the urine under 

 normal conditions .are para-oxyphenyl-propionic acid or hydro- 

 paracumaric acid, and para-oxyphenyl-acetic acid, which results 

 from the former on oxidation. Both are derivatives of ty rosin, 

 and are formed during the process of intestinal putrefaction, as 

 has been shown. Para-oxyphenyl-lactic acid may further be 

 encountered when tyrosin has been administered to animals in 

 large amounts. Under pathological conditions, as in acute yellow 

 atrophy, where leucin and tyrosin may appear in the urine as such, 

 para-oxyphenyl-glycolic acid or oxy-amygdalic acid has also been 

 found. Of special interest also is the fact that in some instances 

 dioxyphenyl-acetic acid (homogentisinic acid) and trixophenyl-pro- 

 pionic acid or uroleucinic acid may occur in the urine. The chemi- 

 cal relationship which exists between these various substances and 

 tyrosin is apparent from their formulae : 



s. 



X CH 2 .CH(NH 2 ).COOH(4) para-oxyphenyl-amino-propionic acid (tyrosin). 



C: 

 2 .CH 2 .COOH(4) para-oxyphenyl-propionic acid. 



CH/ ( H) ' 



^^1\ 



X CH 2 .CH 2 .COOH trioxyphenyl-propionic acid. 



/OH 

 '\CH 2 .CH(OH).COOH para-oxyphenyl-lactic acid 



18 



