Cholesterine is a peculiar spermaceti, or fatty-like substance, found not only in the bile, but also in the nervous tissues, insoluble in water, but soluble in æther or boiling alcohol. When found in a pure state, it is of a yellowish-white color, with the particles arranged in the form of shining thrombic scales. Gall-stones may occur of all sizes, from a pin’s head to that of a hen’s egg. When small, they are generally numerous; in some instances fifty to one hundred being found in the gall-bladder at one time. When several are present in the bladder, they will be more or less angular or polyhedral in form from contact and attrition with one another. Where there are but one or two, the size may be considerable, while the form will be rounded, oblong or pear-shaped, and more or less regular. These bodies, when first removed, are usually heavier than water, but, after being dried, become considerably lighter. They are inflammable, and may be reduced to almost pure charcoal by burning. After having being exposed to the air for some time, they are very liable to crumble more or less completely. _Position._ 1. _Gall-stones may be confined to the gall-bladder._ This is the position in which they are more frequently found. There is every reason to believe that they may remain there for a long time without giving rise to any uncomfortable symptoms. We frequently find them after death in the gall-bladder of persons who, during life, exhibited no symptoms of their presence. They are liable, however, when present, and particularly if numerous or large, to give rise to a sense of weight and dragging in the part, and to occasional attacks of pain, derangement of the stomach and vomiting; and may also excite inflammation and ulceration of the walls of the bladder. The presence of gall-stones, when in large numbers, may frequently be detected through the abdominal walls, as a hard resisting tumor, which, by grasping, may be made to elicit a rattling sensation, like pebbles in a bag. 2. _Gall-stones may become impacted in the neck, or cystic duct of the gall-bladder._ In this case, it is likely to give rise to an attack of biliary colic, with vomiting, etc. As long as it remains in this position there will be no jaundice. Their presence, however, may excite inflammation; yet we sometimes, in post-mortem examinations, find the neck of the gall-bladder blocked up by a calculus, when no symptoms of such an obstruction existed during life. 3. _Gall-stones may form in some of the branches of the hepatic ducts within the liver._ This is not a common point for the formation of these bodies. They are sometimes found, however, in cases of obstruction of the ductus communis. The concretions may be small and rounded, or branching casts of the tubes, resembling pieces of coral.