On the Differences in the Structure of Calculi. 237 



frot diminished in quantity by the use of alkalis, but that it« 

 form and composition are altered, and that it assumes the ap- 

 pearance of a gray powder, and is composed of uric acid with 

 variable portions of the ammoniaco-magnesian phosphate. 



From these facts therefore, it cannot be doubted that the 

 internal exhibition of alkalis often prevents the formation of 

 uric acid, and hence must likewise prevent the increase of ar 

 calculus in the bladder, as far at least as uric acid is concerned ; 

 but it has also been supposed that the alkalis are capable of 

 acting upon the stone itself, and even of effecting its com- 

 plete solution. It is true that if we immerse a calculus, com- 

 posed of uric acid, in a dilute solution of caustic alkali, that 

 it will be slowly acted upon, and after some time entirely 

 dissolved- If however we attend to what would take place ii> 

 the body, we shall find the circumstances very different. 



That alkaline carbonates and sub-carbonates exert no ac- 

 tion upon uric acid I consider to be completely established, 

 both by the experiments of several eminent chemists, and 

 those I have myself made upon the subject; and as there i» 

 at all times a quantity of uncombined acid in the urine, it 

 follows that although the alkali may arrive at the kidneys in 

 its pure state, it will there unite with the uncombined acid y 

 and be rendered incapable of exerting any action upon the 

 ealculusin the bladder. Besides phosphoric acid, the urine 

 always contains a quantity of uncombined carbonic acid ; 

 this is proved by placing a quantity of recently voided urine 

 under the receiver of an air-pump ; during the exhaustion,..* 

 large quantity of carbonic acid gas makes its escape ; and 

 when urine is distilled at very low temperatures, carbonic- 

 acid gas is given off : and also, when lime water is poured 

 into urine, a precipitate appears, consisting of phosphate- 

 and carbonate of lime. 



Lime-water, on account of the insoluble compounds which 

 lime forms with carbonic and phosphoric acids, is evei* 

 more objectionable as a solvent than the alkalis. 



It may however be said, that if these means prevent the 

 increase of a calculus, material relief is afforded to the patient. 

 How far the exhibition of alkaline remedies can be recom- 

 mended upon these grounds, will appear, when the circum- 

 stances- 



