THE URINE. 



341 



sides of the vessel, and scattered over the film on the surface of the 

 urine. By their refractive power they give to this film a glistening 

 and iridescent appearance, nearly always visible at the end of six or 

 seven days. They are colorless, transparent, triangular prisms, gener- 

 ally with bevelled extremities, their edges and angles frequently re- 

 placed by secondary facets. They are insoluble in alkalies, but are 

 easily dissolved by acids, ven very dilute. At first they are of 

 minute size, but gradually increase, so that after seven or eight days 

 they may be recognized by the naked eye. 



As decomposition proceeds, the ammonium carbonate, after saturating 

 all the other ingredients with which it is capable of uniting, begins to 

 be given off in a free form. The urine then acquires an ammoniacal 

 odor ; and a piece of moistened test-paper, held above its surface, will 

 be turned by the escaping alkaline gas. This is the source of the 

 ammoniacal vapor given off wherever urine is allowed to remain and 

 decompose. The change continues until all the urea has disappeared. 



