URINE. 363 



Varieties of Calculus. 



Uric Acid and Urate Calculi. Uric acid and urates constitute 

 the nuclei of a large proportion (81 per cent) of urinary concre- 

 tions. Such stones are always colored, the tint varying from a pale 

 yellow to a brownish-red. The surface of such calculi is generally 

 smooth but it may be rough and uneven. 



Phosphatic Calculi. Ordinarily these concretions consist prin- 

 cipally of " triple phosphate " and other phosphates of the alkaline 

 earths, with very frequent admixtures of urates and oxalates. 

 The surface of such calculi is generally rough but may occasionally 

 be rather smooth. The calculi are somewhat variable in color, ex- 

 hibiting gray, white or yellow tints under different conditions. 

 When composed of earthy phosphates the calculi are character- 

 ized by their friability. 



Calcium Oxalate Calculi. This is the hardest form of calculus 

 to deal with, and is rather difficult to crush. They ordinarily occur 

 in two general forms, i. e., the small, smooth concretion which is 

 characterized as the hemp-seed calculus and the medium-sized or 

 large stone possessing an extremely uneven surface which is gen- 

 erally classed as a mulberry calculus. This roughened surface of 

 the latter form of calculus is due, in many instances, to protruding 

 calcium oxalate crystals of the octahedral type. 



Calcium Carbonate Calculi. Calcium carbonate concretions 

 are quite common in herbivorous animals but of exceedingly rare 

 occurrence in man. They are generally small, white or grayish 

 calculi, spherical in form and possess a hard, smooth surface. 



Cystine Calculi. The cystine calculus is a rare variety of cal- 

 culus. Ordinarily they occur as small, smooth, oval or cylindrical 

 concretions which are white or yellow in color and of a rather soft 

 consistency. 



Xan thine Calculi. This form of calculus is somewhat more 

 rare than the cystine type. The color may vary from white to 

 brownish-yellow. Very often uric acid and urates are associated 

 with xanthine in this type of calculus. Upon rubbing a xanthine 

 calculus it has the property of assuming a wax-like appearance. 



Urostealith Calculi. This form of calculus is extremely rare. 

 Such concretions are composed principally of fat and fatty acid. 

 When moist they are soft and elastic but when dried they become 

 brittle. Urostealiths are generally light in color. 



Fibrin Calculi. Fibrin calculi are produced in the process of 



