266 



PRACTICAL PHYSIOLOGY 



increased excretion of uric acid, but is usually due to a more rapid 

 decomposition of urates. 



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. 



FIG. 160. Calcium oxalate. x 500. 



The crystals are insoluble in acetic acid, which reaction distinguishes 

 them from phosphates or carbonates. They are also insoluble in 

 ammonia, which distinguishes them from urates. 



Microscopically they are seen to be very small octahedra, often 

 flattened along one axis, so that they appear like squares with diagonal 

 lines (hence called "envelope" crystals, Fig. 160). 



4. Stellar Phosphates (Fig. 161). 



Acid urine from a person suffering from disease, or during the administra- 

 tion of certain drugs, may deposit : 



1. Cystin. This forms a deposit somewhat like that of quadriurates. 



