EXAMINATION OP URINARY DEPOSITS. 179 



triple phosphate, &c., is beautifully colored when examined 

 by polarized light; the octahedral variety has little or no effect 

 upon it, being invisible, or nearly so, when the field is dark. 

 If the " dumb-bells" are kept in liquid for any length of time, 

 they gradually pass into octahedra. 



As the crystals of oxalate of lime are very transparent, and 

 about the same specific gravity as the urine, they may readily 

 escape detection, unless some considerable time is allowed for 

 deposition, or the urine is passed through a filter. 



Oxalate of lime is insoluble in water, in acetic and oxalic 

 acids, and in solution of potash; but it is readily soluble in 

 dilute nitric and hydrochloric acids. 



Cystine has occasionally been found as a crystalline deposit 

 and in the form of small calculi. It may be distinguished by 

 being insoluble, or nearly so, in water and dilute acids, but 

 soluble in ammonia, from which small hexagonal crystals are 

 deposited on evaporation. The usual microscopic appearance 

 is represented at a, Fig. 57. At b is the form left from the 

 ammoniacal solution. 



Fig. 57. 



oW (J) 



g>O 



o" i 



AMORPHOUS DEPOSITS consist probably of phosphate of 

 lime, urate of ammonia, urate of soda, fat, or chylous matter. 



Phosphate of Lime. This salt has already been described as 

 existing in urine in conjunction with the phosphate of magnesia. 

 It is thrown down, together with the triple phosphate (before 



