•436 Dr. Prout's Description of an Urinary Calculus [June, 



decided by further observations ; if so, the magnetic needle may 

 be said to have arrived at its maximum variation westward. The 

 mean variation of the raaonietic needle at the close of 1819 was 

 24° 36^ W. 



3 



Article VII. 



Description of an Urinary Calculus, composed of the Lit hate or 

 Urate of Ammonia. By William Prout, M.D. F.R.S* 



M. FouKCKOY had stated that the lithate of ammonia not 

 only frequently enters into the composition of urinary calculi, 

 hnt sometimes constitutes entire concretions.^ Mr. Brande, 

 some years afterwards, called this statement in question, and 

 was induced to conclude from his experiments, " that no sub- 

 stance which can be called urate of ammonia exists in calcuh.":[: 

 In this latter opinion I believe most British chemists have acqui- 

 esced, and Dr. Marcet, in his recent work on this subject, 

 observes, " the presence of this substance (lithate of ammonia) 

 in urinary calculi I still think very doubtful, especially because, 

 since it is so easily discoverable in the excrements of the boa 

 constrictor, it is not probable that the English chemists would 

 have overlooked it so long in the human calculi, which they have 

 so often and so successfully submitted to chemical examination."^ 



From these decided opinions of such eminent chemists, we must 

 conclude that this variety of calculus is extremely rare : to obviate, 

 however, the behef that it does not exist at all, I have been 

 induced to draw up the present account, the object of which is 

 to describe a calculus composed almost entirely of the substance 

 in question. 



Ihis calculus, for wliich I am indebted to my friend Dr. Elliot- 

 son, was extracted in April last by Mr. Cline, jun. from a boy 

 about two years of age, m St. Thomas's Hospital : when entire, 

 it weighed about 50 grs. ; its general shape was ovoid a little 

 flattened ; its external surface was smooth, and of a greenish- 

 clay colour (corresponding nearly to the wax-yelloiv of Werner. ||) 

 It was composed of thin concentric layers, easily separable from 

 one another, and readily breaking into sharp angular pieces, with 

 a compact earthy fracture. Its general colour internally differed, 

 both in shade and intensity from that of its external surface : it 

 might be denominated a pale reddish clay colour (corresponding 



■» From the Medico-chirurgical Transaction', 7ol. x, p. 389. 

 ■)■ Sysleme des Connabsai ces Cliiiniques, loin.x. p. 224. 

 * Phil. Trans, vcl. xcviii. p. 231. 



ij Essay on ihe Chemical History and Medical Treatment of Calculous Disnr- 

 ilers, p. 140, tirst edition. See also Dr. Henry's paper in Ihe present volume, p. 107. 

 I See Werner's Momenclature of Colours, by Patrick S_vir,e. 



