418 Mr. T. Taylor's Observatio?is on Urinajy Calculi 



Mixed Phosphates, —The calculi arranged under this divi- 

 sion are composed throughout of the phosphate of lime and 

 phosphate of magnesia and ammonia mixed in variable pro- 

 portions. Some of these contain thin layers of urate of am- 

 monia, and this salt is frequently present in the fusible cal- 

 culus. 



The number of calculi of this description is rather above 

 the usual average, as the phosphates seldom form the primary 

 deposit. 



It is probable that some of these calculi were formed by 

 the decomposition of urine, which from some cause or other 

 could not escape from the bladder ; such appears to have been 

 the case in two of these specimen?; ; one having been extracted 

 by Mr. Stanley, from a cyst which communicated with a fis- 

 tulous passage leading from the bladder to the perinaeum; 

 and the other having occurred in a patient in whom, on account 

 of an enlarged prostate gland, lithotomy had been performed 

 above the pubes, and through which opening the urine was 

 subsequently expelled. 



Cystic Oxide. — Of these calculi a full description has been 

 given in the Phil. Mag. for April. 



Carbonate of Lime. — This salt rarely forms the principal 

 constituent in calculi from the human subject, and no speci- 

 men of the kind exists in the museum ; it is however very 

 frequently present in small quantities, and generally mixed 

 with the phosphates. 



Purpurate of Ammonia, — Of this singular substance it is not 

 easy to obtain decisive chemical evidence, partly on account of 

 the small quantities in which it occurs, and partly on that 

 of the facility with which it undergoes changes by which its 

 colour is destroyed. I believe I am correct, however, in 

 stating that I have detected it in three instances. In one it 

 formed flesh-coloured layers alternating with the phosphates, 

 in the others it merely coated the calculus. In all of them it 

 was mixed with urate of ammonia. 



With regard to the alternating calculi the table that has been 

 given expresses nearly all that is worthy of particular notice. 

 It may be observed that in no one instance have the phos- 

 phates either pure or in a state of mixture formed the nu- 

 cleus ; indeed this circumstance is so extremely rare, that it 

 has been laid down as a general law by the highest authority 

 on the subject, " that a decided deposition of the mixed phos- 

 phates is not followed by other depositions." There is, how- 

 ever, one specimen in the museum which must be regarded 

 as presenting an exception to this statement. 



The calculus in question consists at its centre of urate of 



