268 



PRACTICAL PHYSIOLOGY 



may exist as long prismatic crystals arranged in star- shaped clusters, 

 hence called Stellar Phosphates (Fig. 191). The crystalline form 

 may also occur in faintly acid urines. 



(6) Ammonium-magnesium Phosphate, Triple Phosphate. -When 

 urine gets stale and ammonia develops in it, a white sediment and 

 a white surface film form. Under the microscope these are seen to be 



FIG. 191. Stellar phosphate of calcium, x 500. 



made up of large clear crystals like " knife rests," or, if excess of 

 ammonia be present, they may look like ' ' 'feathery stars.' ' This latter 

 type can be easily obtained by adding ammonia to normal urine 

 (Fig. 192). 



2. Urate of Ammonia. This looks like the urate of soda crystals, 

 but is associated with crystals of phosphates, and occurs in an 

 alkaline urine. 



3. Carbonates. In the urine of vegetarians these are not un- 

 common. The urine effervesces on adding acetic acid. Micro- 



