URINARY CALCULI. 447 



even by sharp angular projections. It is from the former and 

 most common of these appearances that they have received the 

 name of mulberry calculi. 



The size of these calculi varies from that of a hempseed to a 

 pigeon's egg,, and is occasionally even larger. Thus out of 

 thirty-three calculi of pure oxalate of lime examined by Smith 

 there was only one that weighed an ounce and a half. Their 

 colour varies ; they are white, bright yellow, yellowish-brown, 

 and occasionally dark green. The largest are usually the most 

 darkly coloured. The fracture is usually firm, hard, finely- 

 granular and conchoidal; but calculi have been observed by 

 Berzelius which consisted of an aggregate of closely connected 

 sharp angular crystals. Their specific gravity is higher than 

 that of other calculi. Hence it is evident that the physical 

 characters alone are sufficient to prevent a calculus of this na- 

 ture from being mistaken for one consisting of uric acid or of 

 the earthy phosphates. The chemical characters are, however, 

 equally distinct. It is distinguished from uric acid by its 

 readily burning white before the blowpipe : it is distinguished 

 from the earthy phosphates by its moistened residue exhibiting 

 an alkaline reaction towards red litmus paper, and, if the heat 

 has not been too intense, by its dissolving in hydrochloric acid 

 with effervescence, by ammonia added to saturation producing 

 no precipitate in this solution, but by a deposit being at once 

 observed on the subsequent addition of oxalate of ammonia : it 

 is distinguished from carbonate of lime by its dissolving in 

 hydrochloric acid without effervescence, and by the solution 

 being precipitated by ammonia : and, finally, it is distinguished 

 from urate of lime by its insolubility in boiling water. Although 

 oxalate of lime mixed with a little organic matter (mucus and 

 colouring matter) is generally the sole constituent of mulberry 

 calculi, 1 it is sometimes associated with uric acid, urate of am- 

 monia, or phosphate or carbonate of lime. After what has been 

 already stated, the separation of these substances can scarcely 

 be considered difficult. Ether and alcohol remove fat and ex- 

 tractive matters, water removes the urates, hydrochloric acid 

 the earthy phosphates and oxalate of lime : there can then 

 remain nothing but uric acid with vesical mucus or coagulated 

 albumen, and possibly a little silica. The hydrochloric-acid 

 1 [Our own experience is opposed to this statement.] 



