In the management of wounds and other diseased conditions the main object of the surgeon is to promote the natural reparative process by preventing or eliminating any factor by which it may be disturbed.

#Healing by Primary Union.#—­The most favourable conditions for the progress of the reparative process are to be found in a clean-cut wound of the integument, which is uncomplicated by loss of tissue, by the presence of foreign substances, or by infection with disease-producing micro-organisms, and its edges are in contact.  Such a wound in virtue of the absence of infection is said to be aseptic, and under these conditions healing takes place by what is called “primary union”—­the “healing by first intention” of the older writers.

#Granulation Tissue.#—­The essential and invariable medium of repair in all structures is an elementary form of new tissue known as granulation tissue, which is produced in the damaged area in response to the irritation caused by injury or disease.  The vital reaction induced by such irritation results in dilatation of the vessels of the part, emigration of leucocytes, transudation of lymph, and certain proliferative changes in the fixed tissue cells.  These changes are common to the processes of inflammation and repair; no hard-and-fast line can be drawn between these processes, and the two may go on together.  It is, however, only when the proliferative changes have come to predominate that the reparative process is effectively established by the production of healthy granulation tissue.

Formation of Granulation Tissue.—­When a wound is made in the integument under aseptic conditions, the passage of the knife through the tissues is immediately followed by an oozing of blood, which soon coagulates on the cut surfaces.  In each of the divided vessels a clot forms, and extends as far as the nearest collateral branch; and on the surface of the wound there is a microscopic layer of bruised and devitalised tissue.  If the wound is closed, the narrow space between its edges is occupied by blood-clot, which consists of red and white corpuscles mixed with a quantity of fibrin, and this forms a temporary uniting medium between the divided surfaces.  During the first twelve hours, the minute vessels in the vicinity of the wound dilate, and from them lymph exudes and leucocytes migrate into the tissues.  In from twenty-four to thirty-six hours, the capillaries of the part adjacent to the wound begin to throw out minute buds and fine processes, which bridge the gap and form a firmer, but still temporary, connection between the two sides.  Each bud begins in the wall of the capillary as a small accumulation of granular protoplasm, which gradually elongates into a filament containing a nucleus.  This filament either joins with a neighbouring capillary or with a similar filament, and in time these become hollow and are filled with blood from the vessels that gave them origin.  In this way a series of young capillary loops is formed.