CONCRETIONS. 437 



observing the action of nitric acid and ammonia on a portion 

 of the specimen, and its salts may be demonstrated by extraction 

 with boiling water, and the addition of nitric acid to the nearly 

 dried residue. The presence of oxalic acid may be shown by 

 the digestion of the same portion in hydrochloric acid (the urates 

 having been previously extracted by water) ; on the addition of 

 ammonia, oxalate of lime is precipitated, which, after heating, 

 dissolves with effervescence in the same acid. The presence of car- 

 bonic acid in the specimen may be shown by the effervescence 

 produced on the immersion of a fragment in hydrochloric acid; 

 the presence of ammonia dependent on the ammoniaco-mag- 

 iiesian phosphate, by its development on triturating a portion 

 with caustic potash, the urate of ammonia having been pre- 

 viously removed by boiling water ; the presence of cystin, by 

 digesting the specimen in caustic ammonia, and observing the 

 six-sided plates in which it crystallizes on the spontaneous 

 evaporation of the ammonia ; the presence of cholesterin (in 

 human biliary calculi), of biliphsein (in the biliary calculi of 

 cattle), of hair, and of vegetable fibre, may be determined after 

 some practice by the internal structure and the colour of the 

 concretion. 



In this simple manner we may arrive at a knowledge of the 

 qualitative composition of a calculus ; the analysis is, however, 

 in some respects facilitated by a knowledge of its origin. 

 We know, for instance, that uric acid and its salts occur only 

 in renal, vesical, and arthritic concretions; that the earthy 

 phosphates occur equally in intestinal and vesical calculi ; and 

 that carbonate of lime is a common constituent of concretions 

 in the brain, nose, and salivary glands ; while, on the other 

 hand, oxalate of lime is almost exclusively found in renal and 

 vesical calculi, and cholesterin, bile-pigment, and biliary resin 

 only in gall-stones. 



On vesical and renal calculi in man. 



The concretions of most importance in relation to practical 

 medicine, are vesical and renal calculi and gravel. The con- 

 stituents of urinary calculi, according to the statements of dif- 

 ferent observers, are, 1, uric acid ; 2, urate of ammonia ; 



