On the Differences in the Structure of Calculi. 25$ 



■'■' In what is commonly called a fit of the gravel, a small 

 uric calculus is formed in the kidney, and passes along the 

 ureter into the bladder. 



It-is found from observation, that for some time after a 

 stone has passed from the kidney, the urine is generally un- 

 usually loaJT 1 with uric acid, and deposits that substance 

 upon the nucleus now in the bladder. When this period, 

 which is longer or shorter in different individuals, has 

 elapsed, the subsequent addition to the calculus consists 

 prjtn pahy of the phosphates. 



Where the u ^position therefore to form uric acid in the 

 kidneys is very great and permanent, the calculus found iri 

 the bladder is principally composed of uric acid ; but where 

 this disposition is weak and of short duration, the nuclei^ 

 only s uric acid, and the bulk of the stone is composed of 

 the phosphates. 



Where the increased secretion of uric acid returns at in- 

 tervals, the calculus is composed of alternate layers of uric 

 acid and the phosphates. 



Other small calculi being formed in the kidney, make their 

 way into the bladder, and afford fresh, nuclei ; so that se* 

 veral calculi are sometimes found in the same bladder, and 

 their composition is usually nearly the same. 



In other cases it happens, that a constant increased secre- 

 tion of uric acid is going on from the kidneys, only iri small 

 quantity, which will be more uniformly mixed with the 

 phosphates deposited in the bladder, and where the uric acid 

 predominates, the species of calculus denominated impro- 

 perly, urate of ammonia, will be produced. 



We are entirely ignorant of the cause of the formation of 

 the oxalate of lime, or mulberry calculus. I have frequently 

 looked for oxalate of lime in the urine of calculous patients, 

 tut have never been able to detect it ; and as it does not 

 exist in healthy urine, it must be regarded as a morbid se- 

 cretion. 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 

 casesj as far as my own inquiries go, the persons have been 



much 



