48 ON THE STRUCTURE OF CALCULI. 



case it contains the triple phosphate of ammonia and mag- 

 nesia. 



Effect of alka- When this substance is observed in the urine, the alkalis 

 Ms. 



are recommended. They are exhibited either in a pure' 



state, or as carbonates, and in each instance the uric sedi- 

 ment generally diminishes rapidly, and during the continued 

 use of alkaline medicines, occasionally disappears altoge- 

 ther. 



It however frequently happens, that the matter voided is 

 not diminished in quantity by the use of alkalis, but that 

 its form and composition are altered, and that it assumes 

 the appearance of a gray powder, and is composed of uric 

 acid, with variable portions of the ammoniaco-magnesiau 

 phosphate. 

 Prevent the in- From these facts therefore it cannot be doubted, that the 

 crease of a cal- internal exhibition of alkalis often prevents the formation of 

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

 calculus in the bladder, as far at least as uric acid is con- 

 cerned; but it has also been supposed, that the alkalis are 

 capable of acting upon the stone itself, and even of efTect- 

 Caustic alkali ing its complete solution. It is true, that, if we immerse a 

 dissolves a cal- calculus composed of uric acid in a dilute solution of caus- 

 the bladder. t\c alkali, it will be slowly acted upon, and after some time 

 entirely dissolved. If however we attend to what would 

 take place in the body, we shall find the circumstances very 

 different. 

 Alkaline car- That alkaline carbonates and subcarbonates exert no ac- 

 bonatesdonot. tj on upon uric acid, I consider to be completely established, 

 both by the experiments of several eminent chemists, and 

 Alk li th e ^ ose 1 have myself made upon the subject; and as there is 

 fore cannot act at all times a quantity of uncombined acid in the urine, it 

 in t£f bladder follows » tnat > although the alkali may arrive at the kidnies 

 in its pure state, it will there unite with the uncombined 

 acid, and be rendered incapable of exerting any action npon 

 the calculus in the bladder. Beside 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 ex- 

 haustion, a large quantity of carbonic acid gas makes its 

 escape : and when urine is distilled at very low temperatures* 



carbonic 



