THE URINARY ORGANS. 655 



formed of urinary salts or some foreign body. Their most common constituents are 

 phosphates, uric acid, and urates, and calcium oxalate, or various combinations of these. 



URIC- ACID CALCULI. These are the most common of vesical calculi. In the form 

 of small brownish-red, crystalline aggregations they may be passed as "gravel." The 

 larger uric-acid calculi are not commonly of very great size, are frequently finely nodu- 

 lated on the surface, but may be smooth. The color varies from light yellow to dark 

 reddish-brown ; they are usually dense and lemellated. 



CALCULI FORMED OF URATES. Calculi composed of pure urates are rare, these 

 salts being more commonly combined with uric acid and the phosphates to form the 



FIG. 417. VESICAL CALCULUS. 

 Showing lamellations indicating successive depositions of different texture and composition. 



complex calculi. Sodium urate, in the form of small spined, more or less globular 

 crystalline masses, forms one of the varieties of "gravel." 



PHOSPIIATIC CALCULI. Pure calcium-phosphate calculi are rarely found as whitish, 

 usually smooth, and small lamellated concretions. 



MIXED OR TRIPLE PHOSPHATE calculi are common, and frequently attain large 

 size. These calculi are sometimes pure, but the deposit is more frequently associated 

 with other salts, either as encrusting or intercalated lamellae. Triple-phosphate calculi 

 are usually rough on the surface, of grayish-white color, lamellated, and frequently 

 very friable (Fig. 417). 



CALCIUM-CARBONATE CALCULI. Small gray or white, hard, and usually smooth 

 calculi of pure calcium carbonate occur rarely. Calcium carbonate is sometimes passed 

 as gravel in the form of minute spheroidal bodies, either singly or in clusters. 



CALCIUM-OXALATE calculi (mulberry calculi) are comparatively common, either 

 pure or in combination with uric acid or the phosphates. Calcium oxalate may occur 

 in the form of very small, hard, smooth concretions, or as larger, heavy, hard, finely or 

 coarsely nodulated brown or blackish lamellated masses. The nucleus or some of the 

 lamellae, or both, are often composed of uric acid. 



CYSTIN CALCULI are usually ovoidal in shape, of waxy consistence, of clear or 

 brownish or greenish-yellow color, with mammillated surface and crystalline fracture. 

 Cystiu may be associated in a variety of ways with other calculi. 



XANTHIN CALCULI, which are very rare, are usually of moderate size, smooth, of a 

 cinnamon or cinnabar-red color, lamellated, and oval or flattened in shape. 



