URINARY CALCULI. 565 



monia. Now it is curious, that whenever the urine becomes am- 

 moniacal, the quantity of phosphate of lime which it contains is 

 very much increased. We might, therefore, expect depositions 

 of phosphate of lime in alkaline urine. And I believe that this 

 happens in almost every case. But the deposit is usually in pow- 

 der, and it is evacuated along with the urine, unless a nucleus 

 already exist to which it can attach itself, or unless a quantity of 

 thick mucus sufficient to form with the powder a solid concretion 

 happens to be present. 



Phosphate of magnesia exists in urine in very minute propor- 

 tion, and doubtless in the state of biphosphate. When the urine 

 becomes ammoniacal, this biphosphate is saturated with ammonia, 

 and converted into ammonia-phosphate of magnesia, which, being 

 quite insoluble, is of course precipitated along with the phosphate 

 of lime. It is probable that, when the urine becomes ammoniacal, 

 the quantity of biphosphate of magnesia, which it naturally con- 

 tains, is greatly augmented. Hence the reason of the great quanti- 

 ty of ammonia-phosphate of magnesia found in the fusible calculi. 



It has been shown that urine in certain cases contains a con- 

 siderable quantity of carbonic acid. If we were to admit that 

 when this is the case, the urine (in certain cases at least) may 

 contain bicarbonate of lime, it would explain the very rare for- 

 mation of calculi containing carbonate of lime as one of their 

 constituents. 



It has been shown by Wohler and Liebig that when uric acid 

 is treated with nitric acid, it is (under certain circumstances), con- 

 verted into parabanic acid, and that, when parabanic acid is 

 united to a base, it is converted into oxaluric acid. Now Dr 

 Prout informs us that he has met with nitric acid in certain cases 

 in human urine. We can, therefore, in some measure, account for 

 the formation of mulberry calculi consisting of oxalurate of lime. 

 The formation requires the existence of nitric acid in urine. It 

 is true, indeed, that Wohler and Liebig found it necessary to 

 employ nitric acid of a given density, to apply heat, and to dis- 

 solve in it solid uric acid, in order to obtain parabanic acid. But 

 in the living body the process is much more slow. Nor can 

 there be any reason to doubt that nitric acid, even in the dilute 

 state in which it may exist in urine, may be capable, slowly and 

 silently, to produce the same change on uric acid in the living 

 body, that concentrated nitric acid, assisted by heat, produces 

 upon solid uric acid. 



