Children sometimes die of old age. That is, their original endowment of life energy was so small as to be exhausted during infancy. Others die very soon because of some defective development of a vital organ or organs.

At any period of life the disorders to which we are all subject consist in one or both of the following changes:

1. Disturbance of the action of some organ or organs by a morbid cause.

2. Alteration of the structure or substance of one or more organs; inducing, of course, change also in its action.

To the first of these the term " functional disorders " is applied; those of the second sort are "organic diseases." Temporary changes in the substance or structure of an organ often occur, as when it is inflamed, from which there may or may not follow permanent organic alterations.

Only slight affections of even small parts of the body can take place and last for any time, without involving the general system more or less in disturbance. Also, a disorder beginning in the blood, and thus being a general malady, nearly if not quite always puts some of the functions of the organs out of order. Still some cases do begin in, and chiefly affect, particular organs; these we call local disorders; others begin in the blood, and involve the body in many of its functions; those are well described as general diseases. We will give attention here, first, to the nature of the disturbances coming under the former of these heads.

Local Disorders.

Medical books speak of irritation, congestion (hyperæmia), inflammation, mortification, and degeneration, as affections of organs of the body, Atrophy, hypertrophy, and morbid growths are such also; and less purely local, but often more or less restricted, are dropsical effusions.