DEPOSITS IN THE URINE. 



391 



tion of the urine from which it is deposited. If the urine be allowed to 

 settle in a white earthen or porcelain vessel, and then carefully poured 

 off, the more deeply colored deposits are left as a brick-red stain upon 

 the inner surface of the vessel, forming what is known as the " brick- 

 dust" sediment. 



Deposits of the urates are easily recognized by two special characters, 

 namely : First, they never appear while the urine is still warm, but only 

 after it has cooled ; the urine, when first passed, being always perfectly 

 clear, and becoming turbid on repose, more or less rapidly according to 

 the rate of cooling. Secondly, the urine, after cooling, however turbid, 

 if heated in a test-tube, becomes clear again, usually before reaching 

 the boiling point. Both these characters depend upon the solubility 

 of the urates at high temperatures. 



In rare cases, when a specimen of urine is turbid with the urates and 

 also contains albumen, a double effect may be produced by the applica- 

 tion of heat. When such a specimen is first heated, it is cleared up, 

 owing to the solution of the urates ; but, on approaching the boiling 

 point, it again becomes turbid from precipitation of the albumen. 



The urates are also soluble in the caustic alkalies, so that the ad- 

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

 redissolves the precipitate. The addition of a free acid decomposes it, 

 with the formation of a soluble salt, and the separation of uric acid which 

 afterward crystallizes, as when thrown down in the same manner 

 from normal urine. But the volume of the uric acid thus produced is 

 so much smaller than that of the urates previously disseminated through 

 the urine, that the immediate apparent effect is that of simple solution 

 of the precipitate. A deposit 

 of the urates is accordingly the 

 only one liable to occur in the 

 urine, which is cleared up by 

 the addition of both alkalies 

 and acids. 



Deposits of the urates, when 

 first thrown down, are pulver- 

 ulent in form, presenting un- 

 der the microscope only the 

 appearance of a collection of 

 minute granules. After a day 

 or two they sometimes crystal- 

 lize in the form of bundles or 

 globular masses of radiating 

 needles, often with straight or 

 curved projections, extending 

 from the outer surface. If 

 a few drops of free acid be 

 added to this deposit while under the microscope, the crystalline masses 

 of sodium urate may be seen to grow transparent, and slowly dissolve 



CRYSTALLINE MASSES OF SODITTM URATE, 

 from a urinary deposit. 



