392 THE URINE. 



from without inward, while rhomboidal tabular crystals of uric acid 

 make their appearance in the adjacent fluid. 



Crystals of uric acid sometimes appear spontaneously in a deposit 

 of the urates within a few hours after its formation, owing to the de- 

 velopment of a free acid in the urine ; and they are sometimes formed 

 within the urinary passages, so as to be present when the urine is first 

 passed. Owing to their density and angularity they are the cause of 

 much 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 urates form an abundant light, pulver- 

 ulent, pinkish turbidity ; while the uric acid is a comparatively scanty, 

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

 mulates at the bottom of the vessel, the urates being more slowly depos- 

 ited above it. 



Blood. Urine containing blood is more or less tinged throughout its 

 mass with a dull reddish color which is easily distinguished from that 

 due to a concentration of the normal color of the urine itself. After 

 one or two hours of repose in a cylindrical glass vessel, the blood- 

 globules are slowly deposited ; and when, as frequently happens, they 

 are entangled in minute filamentous coagula, these form a strongl}- 

 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 easily distinguished by microscopic examination, their 

 natural form not being entirely lost even after they have remained in 

 the urine for several hours ; and 2d. The supernatant fluid, when de- 

 canted from the deposit, is found to contain albumen. 



Mucus. The slight quantity of vesical mucus which is normally con- 

 tained in the urine is at first uniformly disseminated throughout its mass, 

 and even after being left in repose is insufficient to produce any well 

 marked or consistent deposit. The light cloudy opalescence, which it 

 forms at the bottom of the vessel, is visible only on close inspection, and 

 is readily disseminated again by the least agitation. But in cases of 

 inflammation of the urinary bladder, the mucus discharged is much 

 increased in quantity and altered in quality. It then appears as a con- 

 sistent mass, which does not mix uniformly with the rest of the urine, 

 but subsides to the bottom as a semifluid deposit. Mucus by itself 

 is transparent and colorless, but it frequently contains a certain 

 number of epithelium cells exfoliated from the inner surface of the 

 bladder; and when crystalline or pulverulent deposits begin to take 

 place in the urine, they occur first in contact with the mucus, so that 

 its surface is often sprinkled with a thin layer of the urates or phos- 

 phates, which give it a partly opaque appearance. It is distinguished 

 by its viscid and semifluid consistency. It is not affected by heat, but 

 is coagulated and shrivelled by the action of alcohol and of nitric or 

 acetic acid. Urine containing mucus is especially liable to rapid de- 

 composition, and often has, soon after being discharged, a peculiarly 

 offensive odor from this cause. 



