ON THE STRUCTURE OF CALCULI. 47 



#ie oxalate of lime, or mulberry calculus. I have fre- th f mulberry 

 quently looked for oxalate of lime in the urine of calculous 

 patients, but have never been able to detect it ; and as it 

 does not exist in healthy urine, it must be regarded as a 

 morbid secretion. Its mode of formation seems to resemble 

 that of uric acid, since small kidney calculi, composed of 

 oxalate of lime, have in a few instances been voided ; and 

 in these cases, as far as my own inquiries go, the persons 

 have been much less liable to a return of the complaint, 

 than where uric calculi have been voided. 



In some rare instances we meet with calculi of the blad- 

 der which are destitute of uric acid, and of oxalate of lime, 

 the nucleus being composed of a little loosely agglutinated 

 ammoniaco-magnesian phosphate, and the whole calculus 

 consisting of that substance, with variable portions of phos- 

 phate of lime: in two cases I have met with calculi of this 

 kind, composed of the triple phosphate only : they seem to 

 be entirely formed in the bladder. 



Having taken this short view of the formation of calculi, Action gf«c&* 

 I shall now inquire into the action of solvents, employed vents ' 

 either with a view of effecting their solution, or of prevent- 

 ing their formation and increase. 



Solvents are of two kinds. 



1. Alkaline. 2. Acid. 



In the exhibition of these, the practitioner is usually 

 guided by the chemical composition of the calculous mat- 

 ter voided by urine. 



The different kinds of gravel, voided by persons labour- Gravel of i*e 

 ing under calculous complaints, may be classed in two di- kmd$ ' 

 visions. 



1, Uric acid, either in a pure state, or with a very small 

 proportion of the phosphates. 



2. The phosphates, either pure, or with a small propor- 

 tion of uric acid. 



The first species, which generally appears in the form of Uric aeii. 

 minute crystalline grains, of a reddish brown colour, or of 

 an impalpable brown powder, is either entirely soluble in 

 pure alkaline solutions, not emitting an ammoniacal odour, 

 in which case it consists of pure uric acid : or it does emit 

 an ammoniacal odour, aud is not entirely soluble, in which 



case 



