The definition of disease we have elsewhere given as being a derangement of the structure or functions of the body. Strictly speaking, any degree of derangement is a diseased condition, although such states are not usually called disease unless the departure from the condition of health is so great as to occasion considerable inconvenience in the way of suffering or danger to life. All modern physiologists agree in this view, although a large share of medical works still retain forms of expression which embody erroneous ideas of disease. In common parlance the term disease is often applied to conditions which are merely symptoms, as dropsy, vomiting, etc., and for the convenience of the reader we shall in this work consider symptoms of this sort in the usual manner; since they require special treatment, and are often the most prominent manifestation of the morbid conditions by which they are produced.

Although there are a great number of individual diseases and morbid conditions, 1,147 different diseases and injuries to which the human body is liable being enumerated in the list prepared by the Royal College of Physicians of London, a careful study of all these different morbid states reveals the fact that the same principle holds good in reference to diseases as in reference to the various organs and numerous parts of the body; namely, that while there arc a great variety of individual forms, there are in fact but a very few primary morbid conditions. The nature of these primary diseases or morbid conditions is by no means so well known as is the minute structure of the anatomical elements of the body, and yet sufficient is known to enable us to greatly simplify our ideas of the nature and proper treatment of disease through an understanding of its simplest elements. In order to give the intelligent reader a better idea of the nature of disease in general, we will briefly consider, before passing to a description of individual diseases, what has been termed the constituent elements of disease or constituent diseases under the two heads, structural derangements and functional derangements.

Structural Derangements Of The Body

It may well be doubted whether there can be any distinct manifestation of disease without a greater or lesser degree of derangement of the structure of organic parts, since function is wholly dependent on structure. For the sake of convenience, we may consider as structural derangements such diseased conditions as involve changes in the tissues of the body to such an extent as to render them perceptible by the senses. Under this head we will first notice -