In some of the open cavities of the body, as in the gall blad der, in the urinary bladder, and in the intestinal canal, there are formed, in some persons, hard, separate, loose masses, which, taking somewhat the character of stones or pebbles, are called calculi--calculas, a pebble. In the gall bladder they usually con sist of a fatty substance, cholesterine. In the urinary bladder they consist of earthy bases combined with an animal acid, or of an insoluble animal acid itself, condensed on a foreign body which acts as a nucleus. In the intestine they consist generally of some foreign substance which has been swallowed in large quantities, such as: magnesia, and which, failing to pass along the intestine, has entered into a concrete or solid mass.
Amongst the local diseases affecting particular organs and parts of the body, is included, in scientific nomenclature, what is called malformation of organs, some error of natural construction by which the proper working of the organic structure is impeded or perverted. A good illustration of this is supplied in those who are born with a defect in the partition wall which separates the right from the left side of the heart in the auricular cavities, of the heart. When this malformation occurs, the venous blood on the right side of the heart, which, naturally, should all pass over the lungs to be oxidized, is allowed, before it reaches the left side, to pass, in part, directly from the venous into the arterial side of the circulation, and so to circulate over the body as a blood im perfectly arterialized. The blood in this state is of a dark or venous color, and the blue condition of body which is present gives origin to the term cyanosis as descriptive of the condition. This is only one malformation, but it is perhaps the best that could be offered for the purposes of practical illustration.