transudation

The liquid portion of the exudation represents something more than the transuded blood-serum, and a certain practical importance results from the distinction drawn between an exudation and a transudation.

The remote parts become swollen, from the distension of the vessels with blood and the transudation of liquid, and eventually solid material from the blood.

To appreciate the conditions under which pathological accumulations of fluid, whether effusions or exudations, may arise, it is desirable to bear in mind the essential conditions which prevail in the occurrence of transudation, since the former are likewise chiefly derived from the blood and are transuded through the walls of its vessels.

The transudation through the vessels takes place chiefly through those with the thinnest walls, the capillaries, although it is probable that a certain degree of transudation may also occur through the walls of the smallest veins.

The causes which are instrumental in promoting the circulation of the blood—viz. the contraction and dilatation of the heart, the contraction of the arteries, the inspiratory action of the thorax, and muscular movements throughout the body—are also essential in producing the flow of lymph; and the existence of pressure upon the h�mic side of the filter is the first feature of importance in occasioning the transudation.