5. Nutritional Changes
will be considered later.
The consequence of persistent hyperemia is transudation—i. e., escape of blood plasm from the vessels into body cavities and tissue interspaces. This leads to consideration under a distinct heading of—
TRANSUDATES AND EXUDATES.
Exudation may occur in vascular and non-vascular, in firm and soft tissues, in, under, and upon membranes. With respect to location, exudates are described as free, when found upon free surfaces or within natural cavities; interstitial, when found between the tissues or parts of tissues; and parenchymatous, when they are situated within the tissues themselves, particularly in epithelial and glandular cells of any kind.
Exudates are serous, mucous, fibrinous, or mixed, the mixed forms including the so-called seropurulent, the mucopurulent, the croupous, and the diphtheritic.
When any exudate contains red globules in sufficient quantity to stain it, it is called hemorrhagic.
Serous transudates from free surfaces are sometimes spoken of as serous catarrhs; when into cavities, as dropsies; when into tissues, as edema; when occurring beneath the epidermis they form serous vesicles or blebs or bullæ.
Fibrinous exudation refers to the fluid which coagulates soon after its exit from the vessels within those spaces into which it has oozed. When flocculi of coagula float in serous fluid it is known as a serofibrinous exudate. Pure fibrinous exudate occurs rarely, save in and upon mucous membranes. The extent to which exposure to the air is responsible for the firm coagulation of the fibrin previously held in solution is uncertain. The most potent factors in producing such coagulation are bacteria, but it is not yet disproved that coagulation may occur without their aid. When such coagulation occurs upon the surface of a mucous membrane it has been spoken of as croupous. When the epithelial covering as well as the basement membrane, and often the submucous tissues, are involved, so that the membrane cannot be stripped off without tearing across minute bloodvessels, the exudate has been known as diphtheritic. These terms may possibly be still retained in an adjective sense as implying the exact location of a surface exudate, but are scarcely to be used in any other significance.
The following table illustrates significant differences whose full importance cannot be impressed before a study of inflammation has been carefully entered upon: