38 



MANUAL OF HISTOLOGY. 



but little according to the nature of the food taken, but much in certain 

 morbid conditions. Uric acid is besides a constituent of blood (Strahl t 

 Lieberkukn, and Garrod). It is also found in the fluids with which 

 many organs are saturated; as, for instance, that of the brain (Muller), of 

 the kidneys and lungs in the ox (Cloetta); and in man, of the spleen 

 (Scherer and Gorup-Besanez). 



Uric acid is a mutation product of azotised tissue-constituents, and as 

 such is widely distributed throughout the animal kingdom. As to its mode 

 of origin, we are unable to point it out, owing to our ignorance of the nature 

 of the matter itself. The fact, already mentioned, that the injection into 

 the body of this acid increases the amount of urea in the urine ( Woliler and 

 Frericlis), seems to point it out as the source of the latter in the system : 

 and the purely chemical decompositions of uric acid, also, which so fre- 

 quently lead to the formation of urea, appear likewise to confirm this view. 



26. 



Hippuric Acid, C 9 H 9 N0 8 . 

 Hippuric acid is a glycin (see below), i.e., an amido-acetic acid = 



or H V N, 

 |CH 2 j 

 1 CO,H 



in which one atom of the hydrogen is replaced by benzoyl (the radicle of 

 benzoic acid), CJELCO, thus 



H 



V CH. 2 



This acid, which takes its name from its occurrence in the urine of 



horses, has the primary crystalline form 

 of a vertical rhombic prism, and sepa- 

 rates from hot solutions in small 

 spangles, or large obliquely streaked 

 four- sided pillars, which have two end 

 surfaces (fig. 1 6). By slow evaporation 

 from dilute solutions, crystals (b) may 

 be obtained resembling in many respects 

 those of phosphate of magnesium and 



0" I I ^* ' II "\^ ammonium, to be described presently. 



\ 1 1 Hippuric, which has much stronger 



II V acid properties than uric acid, may be 



\ dissolved in 400 parts of cold and easily 



& \V in hot water. It is also soluble in 



alcohol, but only slightly so in ether. 

 It forms with alkalies and alkaline 

 earths crystalline salts soluble in water. 

 As to the numerous decomposition 

 products of the acid with which we are engaged, the most characteristic is 

 the transformation which it undergoes on being heated with acids and 

 alkalies : it is split up, namely, into benzoic acid and glycin after taking 

 up water (Dessaignes). 



'Fig. 16. Crystalline forms of hippurlc acid. 

 , a, prisms; 6, crystals formed by slow 

 evaporation, and resembling those of phos- 

 phate of magnesia and ammonium. 



