DISEASES OP THE URINARY ORGANS. 135 



(5) Ammonio-magnesium calculi. — These are of a grayish color and 

 a very rough crystalline surface, which proves very irritating to the 

 mucous membrane. They have a specific gravity of 1.109 to 1.637, 

 and are composed chiefly of ammonio-magnesium phosphate, oxalate 

 of lime, and organic matter, with some little carbonate of lime and 

 magnesia. 



(6) Siliceous calculi. — These are clear, smooth, and hard, and usu- 

 ally spherical. They have a specific gravity of 1.26S to 1.376, and 

 contain 57 per cent of silica with carbonates of iron and magnesia, 

 organic matter, and traces of iron. In other specimens of siliceous 

 calculi there was a specific gravity of 3.122, and there was 79 to 85 

 per cent of carbonate of lime together with carbonate of magnesia, 

 and iron, silica, and organic matter. Others are almost exclusively 

 made of silica. 



(7) Oxalate of lime calculi (mulberry calculi) (PI. XI, fig. 2). — These 

 are characterized by their extremely rough, angular surface, formed 

 by the octahedral crystals of oxalate of lime. Their specific gravity 

 may be 3.441, and they contain oxalate of lime to the extent of 81 

 per cent, together with carbonates of lime and magnesia and organic 

 matter. 



(8) Gravel (pultaceous deposits). — Simple crystals may be met with 

 at any point from the kidneys to the external opening at the end of 

 the prepuce (sheath), and they may appear singly, as crystals, or they 

 may accumulate in masses of fine spherical crystals almost like dirty 

 powdered chalk suspended in water. In the ox this is especially com- 

 mon as a collection in the sheath, distending that into a soft, doughy 

 swelling. 



FORMS OF CALCULI IN DIFFERENT SITUATIONS. 



Apart from the rough crystalline surfaces of the calculi of oxalate 

 of lime and ammonio-magnesium phosphate, the general tendency is 

 to a smooth, round outline. At times, however, they show more or 

 less flattening with rounded angular edges, caused by the contact and 

 mutual friction of two calculi. Sometimes two or more stones lying 

 together become united into one by a new external deposit, and the 

 resulting mass then shows rounded swellings on opposite sides. The 

 large calculi occupying the pelvis of the kidneys usually shows a 

 central part having the outline of the main cavity of the pelvis and 

 two or more projections that have been molded into corresponding 

 branches or channels which lead to corresponding lobes of the kidney. 

 In winter and spring small concretions in the form of plates are often 

 met with in the branches of the pelvis, having been formed and 

 molded in the confined space between the projecting papilla and the 

 surrounding cup-like branch of the pelvis. Finally, the pulp-like 

 deposits in the sheath and elsewhere are made up of globular masses, 

 individually so small as to be often practically microscopic. 



