CALCULI or STONES may occur in any hollow organ in which there is stagnation of the fluid contents together with an excess of some particular substance in solution : they may also occur in the ducts leading from glands from the same cause (see Plate). The chief places where stones occur are in the urinary system and in the gall-bladder.
Calculi in the bladder may have their origin in the kidney, as already stated, or in the bladder itself ; in the latter case they may occasionally form around foreign bodies introduced into the bladder, but in the majority of cases this is not so and the exact method of formation de novo is not yet fully understood, but may be due to the deposition of crystals on organic debris, or on a small focus of organisms. The exact nature of the crystalline material forming the stone depends almost entirely upon the chemical constituents of the urine in which they are formed. In many cases a stone is formed over a period of years, and as the urine may alter its character frequently in this time, a stone is often composed of layers very different in colour, chemical corn position and hardness. Calculi may grow to a great size without causing any symptoms, if smooth, but as they are usually angular or rough on the surface, bleeding generally occurs.
Sometimes a calculus composed almost entirely of one sub stance is found, the substances which give rise to such a stone being uric acid, calcium oxalate, xanthin, cystin or calcium phos phate. More commonly one of these substances forms the nucleus of a larger stone, the outer layers of which may be formed of several different substances such as carbonates and phosphates. The nature of calculi varies according to their composition ; uric acid calculi are hard, smooth and oval or rounded when found in the bladder, or moulded to the cavity when found in the renal pelvis. Pure calcium oxalate stones are rare, but mixed stones in which this substance forms a considerable part are common. Such stones are often formed around a nucleus of uric acid or urates and are distinguished by their dark brown colour and very rough, jagged exterior. Further deposition of other substances may convert the jagged stone into a smooth one. Phosphatic calculi are formed when the bladder is inflamed and are usually rough and often crumble easily. Cystine calculi are very rare ; when they occur they are rather soft and may reach the size of a hen's egg. Xanthin calculi also are extremely rare, only a few isolated specimens having been described in medical literature.
The effect of a large calculus is obstruction : so long as the stone remains loose the obstruction will be intermittent and may largely depend upon the posture of the patient. If the stone be comes impacted or large, obstruction will become complete.
Gall-stones, either single or multiple, may cause no symptoms and are often not discovered during life ; on the other hand they may give rise to serious effects, partly mechanical and partly in flammatory in character. The inflammatory effects cause in flammation of the gall-bladder or cholecystitis. A large stone may become impacted in the neck or the duct of the gall-bladder and cause great distension, a smaller gall-stone may pass out of the gall-bladder and become impacted lower down the common bile duct giving rise to biliary colic and jaundice. In more chronic cases with a subsequent acute inflammation, a gall-stone may ulcerate through either into the peritoneal cavity or into some portion of the gut. In the former case, peritonitis will set in, and in the latter the stone may be small enough to pass right through the bowel or may become impacted and give rise to acute intestinal obstruction. This may also be the result when the stone passes down the duct from the gall-bladder into the gut. Subsequent to passage of a gall-stone through the common bile duct or coincident with the presence of a gall-stone in the gall bladder, localized carcinoma may develop.
A considerable amount of work of different kinds has been done on calculi, especially the commoner ones. Their chemical com position is known moderately accurately; gall-stones, as has been stated, may be formed round a nucleus of organisms, and if these belong to the typhoid group, the stones may be a source of danger by starting an epidemic of typhoid fever at a later date. Certain gall-stones from cases of cancer of the gall-bladder have been found to contain minute traces of radioactive substances. In some cases both gall-stones and urinary calculi will act upon a photographic plate in the dark ; this action is believed to be due to the action of hydrogen peroxide produced from turpines, or to minute traces of ammonia. The effect can be produced either at room temperature or at 37°C ; at the latter temperature a few hours may suffice. (P. L.-B.)