Suppuration is the formation of pus, and is the most frequent termination of acute inflammation, and is a process by which the leucocytes and the embryonic cell formed from the fixed tissue-cells are converted into pus-corpuscles and the intercellular substance of the tissues undergoes liquefaction.

When pus forms an abscess, owing to some chemical substance in its composition, it exerts a solvent action upon the tissues, which is shown by the presence of broken-down tissue cells and remains of tissue, mixed with pus-corpuscles. Suppuration is directly caused by the action of certain specific micro-organisms, and also by certain chemical irritants introduced under the skin. The formation of pus is a result of destructive inflammation, as the presence of such a fluid denotes a loss of substance, which does not occur when a wound heals by the first intention. Under favorable circumstances an inflamed surface, when destruction of tissue has occurred, heals by the process of the second intention, as follows: A soft, red surface of coagulable lymph becomes organized into embryonic tissue, which is known as granulation tissue, and the yellowish fluid, bland in nature, which is present, is pus; these materials, or "products of inflammation," being generated for reparative processes. The granulation tissue is composed of embryonic cells and a network of capillary loops, about which are clustered a number of living leucocytes held together by a delicate intercellular material, by which the tissue receives its supply of nutritive matter from the blood, so that it may become what is recognized later as the cicatricial tissue, or one of a higher organism than the granulation tissue. The healthy granulation tissue is of a variable pinkish, or cherry-red color, the tint depending upon the quality of the blood which its vessels contain, and is of a jelly-like consistence, and somewhat smooth and firm. Its surface, when in a normal condition, is studded over with small conical prominences called granulations, in which very minute vessels are situated very superficially. Healthy granulations are also non-sensitive, elastic, and discharge laudable pus. Unhealthy granulations are coarse, dark red in color, and bleed readily.

Pus of a yellow color is found between the granulations, which vary in size, form and color, a moderate bright-red color being indicative of a healthy healing process.

When there is a want of power in the process of forming the cicatricial or repair tissue, the granulations become large and translucent, and the pus which surrounds them is pale and thin. If the affected surface is exposed to friction, or irritation from other causes, the granulations become extremely small and of a deeper red color than is normal, and at length may disappear at points, leaving grayish spots or smooth patches. If the process of cicatrization is prevented in its first stage, the granulations become large and coalesce, protruding and overhanging the edges of the wound, and forming what is commonly known as "proud flesh." During the entire healing process a flow of pus is going on from the affected surface as a normal act, and the first appearance of it is indicative of repair. Its appearance is also coincident with the organization of plastic lymph. When the suppuration is well established, the heat, tension and swelling of the inflamed part becomes less in degree, and the frequency of the pulse and the temperature of the body diminish. Whenever the granulating surface is formed, union by the second intention, or second adhesion, as it is termed, will take place, if separated surfaces are brought into apposition.