446 MORBID PRODUCTS. 



nucleus and the surrounding strata, they must be analysed 

 separately. 



V. Calculi formed of protein-compounds. Fibrinous calculi, 

 according to Marcet. 



All urinary calculi contain an organic matter, which, by 

 prolonged digestion is soluble in acetic and in dilute hydrochlo- 

 ric acid, from which solutions it may be precipitated by ferro- 

 cyanide of potassium. It is readily soluble in caustic potash, 

 but is insoluble in water, alcohol, or ether : it consists in most 

 cases of the mucus of the bladder, occasionally of albu- 

 men. Marcet described a remarkable calculus consisting en- 

 tirely of protein-compounds, and regarded by him as composed 

 of fibrin. It had the appearance and consistence of yellow 

 wax ; its surface was irregular, but not rough -, internally it ex- 

 hibited a fibrous character, and was, to a certain degree, elastic. 

 When burned it evolved the odour of burning horn, and left a 

 porous carbonaceous residue. It was insoluble in alcohol, 

 ether, or water, but dissolved in caustic potash, from which it 

 was precipitated by hydrochloric acid. It dissolved slowly in 

 nitric acid, and when boiled in acetic acid, swelling previously 

 to dissolving. It was precipitated from its acetic acid solution 

 by ferrocyanide of potassium. In its solubility in nitric acid it 

 does not (as Berzelius remarks) correspond very well with the pro- 

 perties of fibrin ; its characters, as given by Marcet, lead more 

 to the supposition that it was vesical mucus. Morrin has 

 likewise described a calculus remarkable for the quantity of 

 organic protein-like substance contained in it. It was asso- 

 ciated with phosphate of lime, and amounted in the nucleus to 

 only 10g, in the second layer to 18g, and in the third to 70 of 

 the weight of the calculus. Alcohol took up a little fat. The 

 substance was slightly soluble in acetic, more so in nitric 

 acid : in caustic potash it swelled, became viscid, and partially 

 dissolved. 



Incombustible or partially combustible Calculi. 



VI. Calculi of oxalate of lime are next in frequency to those 

 of uric acid and the earthy phosphates. Their form is very 

 characteristic; they are usually spherical, but their whole 

 surface is studded by verrucose, tuberculated elevations, or 



