ON THE STRUCTURE OF CALCULI. 3J 



This is the largest proportion of animal matter which I 

 have met with. 



A small calculus from the kidney, weighing 3*7 grains, Sometimes in 

 afforded by a like treatment 3-5 grains of uric acid, so that T^J^f 11 

 it was nearly a pure specimen of that substance. 



The largest calculus of this kind which I have examined 

 weighed seventeen grains ; much larger ones have been 

 found, but there is no evidence of their not having remained 

 in the urinary passages for some considerable time. Thus 

 Dr. Heberden mentions one weighing twenty-eight grains*. 



It often happens that the ingredients are not united toge- Sand, 

 ther so as to form a calculus, but are voided in the state of 

 a fine powder, commonly termed sand. This consists either phosphates 

 of uric acid, or of the ammoniaeo-magnesian phosphate, found in this, 

 alone, or with the phosphate of lime. 



I am induced to believe, that the last mentioned sub- *wt n °t in the 

 stances, although the production of thekidnies, and held in 

 solution, are never met with in a separate state, till the urine 

 has been at rest, and therefore calculi from the kidnies are 

 never composed of the phosphates. 



In a few instances, calculi from the kidnies composed of pxalateof 

 oxalate of lime are voided ; *but this is a very rare occurrence. lime * 

 Of three preserved in the Hunterian collection, two are ex- 

 tremely small and hard, having an appearance of being made 

 up of several smaller calculi, of a dark brown colour. The 

 third is of the size of a small pea, its surface smooth, and 

 of a gray colour, not very hard. 



Sect. II. Of Calculi which have been retained in the 

 Kidney. 



When one or more of the calculi described in the preced- Calculi detain- 

 ing section are detained in the infundibula or pelvis of the ne m * e 

 kidney, it frequently happens, that they increase in that si- 

 tuation to a considerable size. 



This increase is of two kinds. 



I. Where there is a great disposition to the formation of 

 uric acid, the calculus consists wholly of that substance and 

 animal matter, so as frequently to form a complete cast of 

 the pelvis of the kidney. 



* Comment on the Hist, and Cure of Diseases, 3d. edit. p. 88. 



2. Where 



