168 On the Differences in the Structure of Calculi. 



blacken and emit a strong odour of burning animal matter, 

 very different from that of pure uric acid. This arises from 

 a variable proportion of animal matter which they contain, 

 and which occasions the loss in the analysis of these calculi. 

 Its relative quantity is liable to much variation, as may be 

 seen from the following statements. 



A calculus from the kidney, weighing seven grains, was 

 dissolved in a solution of pure potash. A quantity of mu- 

 riatic acid (rather more than sufficient for the saturation of 

 the potash) was added, and the precipitate of uric acid thus 

 obtained weighed when dry 4*5 grains. No other substance, 

 except animal matter, which was evident on attempting to 

 obtain the muriate of potash, could be detected, consequent- 

 ly the composition of this calculus was as follows: 



Grs. 



Uric acid - 4*5 

 Animal matter 2*5 



7-0 



This is the largest proportion of animal matter which I 

 have met with. 



A small calculus from the kidney, weighing 3' 7 grains, 

 afforded by a like treatment 3*5 grains of uric acid, so that 

 it was nearly a pure specimen of that substance. 



The largest calculus of this kind which I have examined 

 weighed seventeen grains ; much larger ones have been 

 found, but there is no evidence of their not having remained 

 in the urinary passages for some considerable time. Thus 

 Dr. Heberden mentions one weighing twenty -eight grains*. 



It often happens that the ingredients are not united toge- 

 ther so as to form a calculus, but are voided in the state of 

 a fine powder, commonly termed sand. This consists either 

 of uric acid, or of the ammoniaco-magnesian phosphate, 

 alone, or with the phosphate of lime. 



I am induced to believe that the last-mentioned substances, 

 although the production of the kidneys, and held in solution, 

 are never met with in a separate state till the urine has been 



* Comment, on the Hist, and Cure of Diseases, 3d edit. p. 88. 



at 



