URIC ACID AND URATES. 207 



URIC ACID AND URATES. 



The properties of these compounds have been given 

 before. As a sediment, the free acid and its salts differ 

 from all others in being colored yellow to brown. They 

 are not abnormal in urine unless they are present as solids 

 when the urine is passed, or are deposited within a few 

 hours, since normal urine throws down uric acid on fer- 

 mentation. The precipitation of these compounds is 

 largely effected by a concentration or an increase in the 

 acidity of the urine. The normal or dibasic urates are 

 readily soluble in water, and do not occur in sediments. 

 When the acidity of the liquid is increased, either by 

 fermentation or by the addition of an acid, half the base 

 is taken from these salts, leaving the monobasic or acid 

 urates, which are soluble with much more difficulty. If the 

 acidity becomes still greater, all the base is removed, leaving 

 the free acid, which is only very slightly soluble in water. 

 Of course, a decrease in the volume of water would be ac- 

 companied by a corresponding increase in precipitated 

 uric acid and its compounds. Hence a sediment of these 

 may appear in the urine without signifying that an in- 

 creased quantity has been formed in the body. Thus, they 

 are common in fevers, when the urine is of small volume 

 and concentrated. Less uric acid is formed in the body 

 with a vegetable diet than with one of meat. 



Uric acid and urates as sediments occur mostly in 

 acid urine and can be usually identified microscopically. 

 (Plate II, 11.) The color is characteristic. The acid is 

 always crystallized, commonly oval or diamond shaped, 

 sometimes visible to the naked eye, often in clusters or 

 rosettes. The urates are commonly salts of sodium, potas- 

 sium, or ammonium. They may be amorphous when ex- 



