Comprehending under this head both gall-stones and other concretions, we will first, then, observe that some hepatic concretions cannot pass from the place of their origin into the intestines, but only such as are situated in the main branches of the liver, in the gall bladder, etc.; that when their size is not disproportionate to the diameter of the ducts, they pass with facility, but when their dimensions are larger than those ducts can naturally admit, the latter become stretched and dilated, whence arise the sharp colicky pains which usually attend the disorder. Now as all crystallisations depend upon the fluids in which they form, and from which they receive their crystallising elements, it must be evident that inasmuch as the fluids of the hepatic organs differ in their constituent principles from the fluids contained in the intestinal canal, the concretions produced in the first system must differ from those originating in the second, whilst the hepatico-gastric calculi will combine the nature and properties of both together.

Arriving at this conclusion, the fluid from which hepatic concretions are formed is unquestionably the bile, either some or all of its ingredients entering into their composition. Indeed, at one time hepatic calculi were generally considered as being simply condensed indurated bile.

From investigations made in more modern times, however, when the art of analysis has attained a precision of which the old chemistry school was not susceptible, it appears that although biliary calculi yield the same products as the bile, there is contained in them more or less of a peculiar substance which was considered to be very similar to spermaceti, but which has since been proved to be cholesterine. Now the presence of this substance in the concretion is of such importance that when it is abundant and in large proportion the calculus is regular and the crystallisation well finished, and when it is small the crystallisation is confused and disordered; the calculus only exhibiting an irregular misshapen concretion.

According to other authorities, biliary concretions in general are composed of the yellow colouring matter of the bile and cholesterine, the latter predominating, and being sometimes in a state of purity.

While the hepatic system contains a fluid which is always nearly of the same quality, namely the bile, the alimentary canal contains a hundred different fluids, and is continually occupied by substances of various natures, kinds, and properties, consisting of food, drink, and diverse secretions. All the principles which are to serve for the formation and renewal of the different species of living solids, and of the many kinds of fluids, at first remain more or less time in the alimentary canal, and there undergo peculiar changes. All the principles which under different circumstances may contribute to the production of morbid concretions, either in the gall bladder, the urinary bladder, the kidneys, or in any other part of the body where they ever occur, pass at first into the intestinal canal, where they continue for some time. Such a multiplicity of principles, disposed to crystallise and be converted into calculi, would almost daily produce these concretions in the bowels, were there not many circumstances which counteract this tendency; as, for instance, exercise; the incessant motion of the matter itself along the intestinal tube; the variety of these elements, whereby their natural tendency to unite is disturbed; and the decomposing and recomposing influence of the gastric secretions, whereby parts are united, disposed of, dissolved, and analogous matter kept divided. But whenever these circumstances are not actively operating, as may be the case in a noose or fold of the bowels, or in some preternatural spot belonging to them; whenever the intestinal fluids undergo such an alteration that the production of these concretions cannot be prevented, or, lastly, whenever some favourable circumstance, such as an extraneous nucleus, forms a centre of reunion which is most disposed to crystallise, the earthy and mucilaginous substances are attracted together, and produce more or less perfect crystallisations.

Millers' horses are subject to alvine concretions formed of collections of the grit of the stone-dust in the mills, taken into their stomachs when fed upon soft bruised foods. In cows and sheep the concretions are found often in the alimentary canal, consisting of hairs and anything that will form a nucleus; of course if these are evacuated so much the better, but as a rule the patient dies after frequent attacks of colic and indigestion and constipation.