1820.] Dr Henry on Urinary Calculi. Ill 



nucleus composed chiefly of uric acid. It appears then that in 

 a very great majority of cases, the disposUion to secrete an 

 excess of uric acid, has been the essential cause of the formation 

 of stone ; and it becomes important to inquire what are the cir- 

 cumstances that contribute to its excessive production, and by 

 what plan of diet and medicine the tendency to its too great 

 secretion by the kidneys may best be counteracted or removed. 

 This inquiry, however, is not within the scope of the present 

 essay, which is hmited to the chemical composition of the con- 

 cretions when actually formed. 



Of Uric Acid Concretions. 

 It has never yet occurred to me to examine a calculus com- 

 j)osed of this acid in a state of absolute purity. Of the concre- 

 tions \yhich 1 have classed under this head, a considerable 

 number, after the action of pure potash, have left an insoluble 

 residue of the earthy phosphates ; and from the solution of those 

 even, which have entirely dissolved in that menstruum, I have 

 in no case been able to recover by the addition of acids, a quan- 

 tity of uric acid equivalent to the weight of the calculus dissolved. 

 The utmost that I have ever obtained has been 92 parts from' 

 100 of an uric concretion. On this subject, therefore, my expe- 

 rience entirely agrees with that of Mr. Brande.* The loss 

 doubtless arises from the decomposition of animal matter by the 

 alkah. This, as I have stated in my Thesis, is partly urea, 

 which I found may be separated by digesting the powdered 

 calculus in alcohol, and evaporating the solution .f It is not 

 however, to urea that the colour of uric acid calculi is to be 

 ascribed, but rather to the other substances which in urine o-ene- 

 rally accompany it ; for it has been shown by Professor Berzelius 

 and by Dr. Prout that pure urea is destitute of colour. In one 

 instance only I have observed a vesical calculus composed 

 chiefly of uric acid, to be of the whiteness of chalk ; and from 

 this the action of alcohol did not extract any portion of urea. 

 Gelatine I have never been able to discover, by applying- its 

 appropriate test to water which had been digested in the pow- 

 dered calculus ; but the presence of albuminous matter appears 

 to me to be indicated by hght flocculi, which sometimes float 

 over the uric acid, when precipitated by acids from its solution 

 in alkali. It is probable, however, that the characteristic ingre- 

 dient of urinary calculi does not necessarily require a cement to 

 bind It together, but that the aggregative attraction of its par- 

 ticles is sufficient to unite them into a compact mass. AH 

 curative plans, therefore, which have in view the removal of a 

 cementing ingredient (the mode in which Haller and Hartley 

 explained the action of alkaline solvents) appear to me to be 

 without probable grounds of success. 



• Phil. Tub,. 1808. + Di.sert Inaug. 1£0T, p. S9. 



