164 



UKEA. 



/NH.CO 



(oxalic acid) gives parabanic acid, CO V I ; of tartronyl (tar- 



X NH.CO 



tronic acid), dialuric acid, CO v /CHOH; of mesoxalyl 



NH.CO 

 X NH. CO x 

 (mesoxalic acid), alloxan CO x / CO. These substances are 



XH . CO 



interesting as being also obtained by the artificial oxidation of uric 

 acid. The close chemical relationship of urea to uric acid will be 

 explained below. 



Uric acid. C 6 H 4 X 4 3 . 



The chief constituent of the urine in birds and reptiles; it 

 occurs only sparingly in this excretion in man (-2-1 grm. in 24 

 hours) and most mammalia. It is normally present in the spleen, 



Rapidly separated. 

 FIG. 17. CRYSTALS OF URIC ACID. 



Slowly separated. 

 (Krukenberg after Kiihne.) 



and traces of it have been found in the lungs, muscles of the heart, 

 pancreas, brain, and liver. Urinary and renal calculi often consist 

 largely of this substance, or its salts. In gout, accumulations of 

 uric acid salts may occur in various parts of the body, more espe- 

 cially at the joints, forming the so-called gouty concretions. 



It is when pure a colourless, crystalline powder, tasteless, and 

 without odour. The crystalline form is very variable, differing 

 according to the concentration of the solution from which the 

 crystals are obtained, the rate at which they are formed, and 

 whether they are separated out spontaneously or by the addition 

 of acids to either solutions of the acid or to urine. Hence it is 

 extremely difficult to illustrate them within reasonable limits, 

 and for figures of the various possible forms some special work 

 must be consulted. 1 The impure acid crystallises much more 



i See Ultzmann and K. B. Hofmaim, Atlas der Harnsedimente, "Wien, 1872. 

 Also Funke, Atlas d. physiol. Chem. Leipzig, 1858. 



