NATURE OF DISEASES. 23 
CHAPTER II. 
NATURE OF DISEASES. 
Tue disorders which may occur in either sex and at any period of life consist 
of disturbances of the action of some organ or organs by morbid causes, or alter- 
ations of the structure or substance of one or more organs, which also induce 
changes in the action of the same. The first of these are termed “ functional dis- 
orders,” the others are “organic diseases.” So intimate is the relation existing 
between all of its parts, that only mild and very limited affections can occur with- 
out the whole system becoming involved and sharing in the disturbance. On the 
other hand, when a disorder first affects the blood, and is therefore of general 
character, nearly if not quite always one or more important organs are very soon 
deranged. In the first instance, in which the trouble begins in particular organs 
and chiefly affects them, the cases belong to the so-called local disorders or dis- 
eases; whereas those that start in the blood and involve the body in its many 
functions are termed general diseases. 
Among the terms in use and applied to various affections of organs of the 
body are irritation, congestion, inflammation, mortification, degeneration, atrophy, 
hypertrophy, and morbid growths. In the action of a mustard-plaster, the con- 
ditions covered by several of these terms appear. Very soon after it has been 
applied, the skin is stimulated and the circulation quickened in the parts imme- 
diately beneath the plaster. Thus far the action may be said to be a healthy 
one. If, however, the mustard be allowed to remain on a short time longer, and 
until it has caused pain and soreness, then the condition exists which well illus- 
trates irritation. Now have it remain on still a while longer, and it will produce 
inflammation. 
The terms congestion and hyperemia are synonymous, the latter being more 
in use among physicians. It means, literally, an excessive amount of blood in 
certain vessels, especially the smallest, called the capillaries. Hyperaemia, or con- 
gestion, exists when more blood than usual is flowing through a part, — it is then 
termed active hypereemia,— or when there is a collection of more than the 
normal amount of blood in a part, the same being as it were stagnant and not 
circulating actively, which condition is known as passive hyperemia. In con- 
tradistinction with this there is the term local anemia, which is a deficiency of 
blood in the part to which the term is applied. 
When a part becomes red, swollen, and painful, and there is unusual heat in 
