THE UEIXE. 



337 



FIG. 82. 



The urates are also soluble in caustic alkalies, and the addition of 

 a few drops of a solution of sodium or potassium hydrate redissolves 

 the precipitate. Free acids, on the other hand, decompose it, with the 

 formation of a corresponding sodium or potassium salt, which remains 

 in solution, and the separation of uric acid, which slowly crystallizes. 

 But the volume of uric acid produced is so much smaller than that 

 of the urates previously disseminated through the urine, that the only 

 effect immediately apparent is 

 that of solution of the precipi- 

 tate. A deposit of the urates is 

 accordingly the only one liable 

 to occur in the urine, which is 

 cleared up by both alkalies and 

 acida 



Deposits of the urates, when 

 first thrown down, are pulveru- 

 lent in form, presenting under 

 the microscope the appearance 

 of minute granules. After a day 

 or two they sometimes crystal- 

 lize in globular masses of radi- 

 ating needles, often with straight 

 or curved projections from the 

 outer surface. If a free acid be 

 added to this deposit, tin- crys- 

 talline masses grow transparent, and slowly dissolve from without 

 inward, while rhornboidal tabular crystals of uric acid appear in the 

 adjacent fluid. 



Crystals of uric acid sometimes appear in a deposit of the urates 

 after a few hours, owing to the development of a free acid in the urine ; 

 and they are sometimes formed within the urinary passages, so as to be 

 present in the urine when )>;t < !. Owing to their density and angu- 

 larity they cause an irritation to the mucous membrane of the bladder 

 and urethra, and are known as the "gravel" of the' urine. In a 

 mingled precipitate of the urates and uric acid, the uric acid is a scanty, 

 dense, deeply colored, crystalline deposit which sinks rapidly and accu- 

 mulates at the bottom of the vessel, while the comparatively light and 

 pulverulent urates are more slowly deposited above it. 



Blood. Urine containing blood is more or less tinged throughout 

 with a dull reddish color. After one or two hours of repose in a cylin- 

 drical vessel, the blood-globules are slowly deposited ; and the minute 

 filamentous coagula with which they are frequently entangled form a 

 strongly colored red layer at the bottom of the vessel. The nature of 

 the deposit is recognized by two well-marked characters, namely : 1st. 

 The blood-globules are distinguished by microscopic examination, their 

 form not being entirely lost even after remaining in the urine for sev- 



W 



CRYSTALLINE MASSES OF SODIUM URATE. from 

 a urinary deposit. 



