This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
Exudation is a process by which the corpuscular elements of the blood and the liquor sanguinis pass through the walls of the blood vessels into the tissues beyond, and results from changes in the walls of the vessels, which permit the oozing of the blood through their walls - "the loss of the power by the vessels of resistance to dilatation, and the loss of vital power, in consequence of which leakage takes place." The symptom of swelling is in great part due to exudation. The exudation in what is termed "healthy inflammation," and known as plastic or coagulable lymph, seen on the surface of a recent wound or in the form of swelling around a centre of imflammation, is a mild and unirritating product, the function of which is to form new tissues for repair, called at first granulations. Inflammatory exudations from free surfaces of mucous membranes contain mucus, and a substance known as mucin, in the form of filaments, insoluble in acetic acid. The inflammatory effusion known as plastic or coagulable lymph, the true indicator of a healthy constructive process, is soon converted from a jelly-like substance, by the germinal power, into a mass of living cells, through which other minute cells, which are to form the capillaries, make their way like a small stream, the primitive living cells flattening out, and making walls, apparently, for the forming vessels. These new capillaries penetrate the mass of germinal cells in large numbers, like delicate connecting threads, and furnish the blood supply to the organizing mass, which becomes converted into new or young connective tissue. This tissue drawing and binding together the opposite sides of the wound then becomes the cicatricial tissue, which originates from the cement-like material furnished by the inflammatory exudation. The cicatricial tissue becomes invested, in the case of oral mucous membrane, with epithelium, by a similar process of cell growth and development; and this is the process of union by the first intention. The cicatrix or scar is redder than natural, owing to the large number of vessels: but when the supply of blood is no longer needed in such quantity as is at first necessary, the capillaries diminish and disappear, so that the cicatrix grows paler and of smaller bulk. In the case of an abrasion of the skin, the exuding plastic lymph dries upon the denuded surface when not disturbed, and forms a protecting crust, which at length falls off, exposing a reddish surface covered with epidermis. In the case of the oral mucous membrane, a like result is produced under the protection of the mucous secretions peculiar to such a tissue.