52 MICROSCOPICAL DIAGNOSIS. 



granular in character or it may occur as small spherical masses 

 in the form of dumb-bells. Phosphate of lime is precipitated by 

 alkalies as an amorphous powder. 



THE CRYSTALLINE AND GRANULAR DEPOSIT. 



Uric Acid is deposited as a sediment only when the urine has 

 an acid reaction. The sediment is never colorless, although it may 

 have but a pale-yellow color. It has, usually, either a deep yellow, 

 an orange, or a brown color. The unaided eye is generally suffi- 

 cient to identify the presence of uric acid, for it is the only sub- 

 stance giving a spontaneous deposit of brown crystals. The 

 crystals usually lie scattered as colored specks on the sides of the 

 glass vessel, forming also a layer of deposit at the bottom. It ap- 

 pears in many different forms under the microscope, the more com- 

 mon being that of smooth tables of the rhombic form. These 

 rhombic crystals are modified by having their angles rounded off in 

 such a way that spindle-shaped crystals are produced. Other varie- 

 ties exist, as dumb-bells, six-sided plates, rectangular tables, saw- 

 shaped, fan-shaped, etc. If there be any doubt as to the nature of 

 any particular form it is only necessary to dissolve the sediment on 

 the glass-slide in a drop of potassic hydrate, and then add a drop of 

 hydrochloric acid, when the usual form will appear. Uric acid is 

 insoluble in hot water but soluble in alkalies, potash, soda and 

 ammonia. Some of the sediment, supposed to be uric acid, may be 

 placed on a slide and a drop of strong nitric acid added to it. After 

 evaporating it to dryness, one or two drops of ammonia are added. 

 If a purple-violet or violet- red color appears it denotes the presence 

 of uric acid or a urate. In testing for an excess or for a deficiency 

 of urea the quantity of urine passed in twenty-four hours should be 

 taken into account. If the amount passed be below the average it 

 should be diluted with water until it reaches that point; if the quan- 

 tity be in excess of this average then it should be evaporated to that 

 point. After proceeding thus, if the urine has a specific gravity 

 over 1030, an excess of urea may be the cause. To test for this, 

 place enough of the urine in a test-tube to fill it an inch in depth; 

 add to this one-third its bulk of pure nitric acid, and set in a cool 

 place, or in cold water, better always in water near the freezing- 

 point. If crystals of nitrate of urea form in a few moments then an 



