The size of the masses may be from a pea or smaller, up to calculi of six inches in diameter.
In number there may be a single calculus or there may be an indefinite quantity. Zundel counted 400 in a single colon, and Gurlt 1,000.
Composition. They are usually composed of phosphate of lime and of magnesia, of ammonio-magnesian phosphate, with a little silica, mucus, epithelium, and organic matters from the ingesta. Traces of sodium chloride, and iron oxide may also be present.
The phosphates of lime, magnesia, and of ammonia and magnesia usually constitute the main part of the calculus. Fürstenberg found specimens in which the ammonio-magnesian phosphate amounted to 72 to 94 per cent.
The calculi containing an excess of ammonio-magnesian phosphate tend to assume a crystalline or coralline form which causes them to be specially irritating to the mucosa. When broken they show a radiated structure from the centre to the circumference in addition to the concentric rings. These are usually of a yellowish brown or a gray color and have a specific gravity of 1694 to 1706.
Calculi in which the common phosphate of lime abounds are likely to be smooth on the surface and on section show the concentric rings more distinctly and the radiating lines less so. The brownish calculi of this variety are much more compact, and harder than the crystalline or mulberry calculi, and have a higher specific gravity—(1823).
Bluish calculi with a smooth glistening surface and lower specific gravity—1681—, have been found of small size and in great numbers in the colon (1000 in the colon, Gurlt).
In some calculi there is a large admixture of alimentary matters, and a low specific gravity (1605 to 1674). These were designated as pseudo calculi, by Fürstenberg.
In still other cases a calculous looking mass, when broken into, is found to be composed of a mass of dried alimentary matter enclosed in a thin layer of lime salts. These have a low specific gravity (1446 to 1566) and have been named concretions by Fürstenberg.
Causes. As a large proportion of the calculus is phosphate of lime or ammonio-magnesian phosphate, we must look for the source of these in the food and then at the conditions which determine their precipitation.