disease (embolism, metastasis); in still other cases the impairment of the healthy function in one organ acts injuriously on another, as when emphysema or other disease of the lungs forces the blood back upon the heart causing dilation with atrophy of the walls. _Previous disease in a tissue_ leaves for a time an impairment of structure and function which may become the essential predisposing cause of the effective operation of a morbific factor. _Mechanical_ action on a part may predispose to disease, as for example, by reducing its circulation and nutrition and thereby directly impairing its power of resistance to other inimical agencies. Not infrequently a pus microbe lies deep in the cuticle or even in the tissues without harm, until there occurs a bruise, or a bony fracture when it at once develops a focus of purulent infection (abscess). =Exciting Causes= are the immediate causes of particular diseases. Like the predisposing causes they may be _intrinsic_ or _extrinsic_, and the first may be =inherent= or =acquired=. Among =inherent= causes are certain of those already named as predisposing causes, but which have come to be forcible enough to develop disease without the intervention of any other observable factor. Thus a _hereditary_ monstrosity (redundancy or defect), will appear in successive generations without any apparent additional cause. The appearance of white calves in herds of black cattle, after the whitewashing of their stables shows a similar hereditary operation though the result is not in this case pathological. The birth of blind foals from blind sires or dams, or of foals with distorted feet from mares suffering from severe chronic foot lameness are true pathological sequences, in which the exciting cause is hereditary and operates during intrauterine life. _Dentition_, as an attendant on early life is often a directly exciting cause, from direct injury by entangled or retained teeth that should have been shed, by fever aroused by the active local changes, or imperfect mastication or insalivation leading to consequent indigestion; in puppies and kittens convulsions are not uncommon as a result.