440 



PRACTICAL PHYSIOLOGY 



2. Uric Acid. This may be split off from the urates as described on 

 p. 424. It appears as a cayenne pepper-like sediment, and has a definite 

 crystalline appearance under the microscope (Fig. 245). The crystals 

 may vary much in shape, but are always large and tinged a reddish 

 colour. The most usual shapes for the crystals to assume are " sheaves," 

 "whetstones," "rhombic tables," and sometimes "dumb-bells." The 

 presence of the crystals does not necessarily indicate an increased 



FIG. 252. Calcium oxalate. x 500. 



excretion of uric acid, but depends on the concentration and acidity 

 of the urine. 



3. Calcium Oxalate. This is usually a scanty deposit, adhering to 

 irregularities on the surface of the glass of the urine jar, or forming 

 a glistening layer on the top of the mucous deposit that settles at the 

 bottom. 



The crystals are insoluble in acetic acid. This reaction distinguishes 

 them from phosphates or carbonates. They are also insoluble in 

 ammonia, and are thus distinguished from urates. 



