The secretion of pus has been looked upon as a general prevention of many or of all the causes of disease. Hence issues have been made to keep off universal as well as local diseases. However, the use of pus is perhaps unknown, for it is formed most perfectly from healthy sores, and in healthy constitutions, and large discharges from parts not essential to life produce very little change in the constitution, and as little upon being healed up, whatever some may suppose to the contrary.

When the surface of a sore is left uncovered, the thin part of the matter evaporates, and the thick part dries and forms a scab. Nature, therefore, seems to have designed that one use of pus should be to make a cover, or protection, for ulcerated surfaces. That being so, I must herein lodge my dissent from the theory that the natural healing of a sore under a scab usually takes place more quickly than when the proper dressings are employed.

Now, among the secondary uses of suppuration may be mentioned that of opening a communication between a disease and the external surface of the body, and that of leading to the formation of a passage for the exit of extraneous bodies, etc.

Though an abscess is sometimes dispersed by its contents being absorbed, this is not the usual course of the case, and the tumour, instead of diminishing, generally continues to increase, instead of subsiding or remaining stationary. Under such circumstances the pus commonly advances either to the skin or a mucous surface, in which an outlet for it is produced by an ulcerative process. Here, then, we find that pus is subject to the general law of the animal economy, which tends to expel from the body all deleterious substances capable of irritating and disturbing its textures. It is scarcely necessary to observe that when pus makes its way into a cavity, passage, or organ lined by a mucous membrane, it finds almost as ready an outlet from the body as if the abscess had taken its still more frequent course to the cutaneous surface If an abscess be near a mucous texture, then nature will often make the pus take this direction to discharge itself instead of conducting it to the skin, which may be more remote. But we do not remark a similar tendency of abscesses to make their way into cavities invested by a serous membrane, because, as this always constitutes a close sac, the advantage of an outlet for the purulent matter would not thereby be obtained. Illustrations of this disposition are afforded in abscesses in the vicinity of bones, or in the parietes of the abdomen or chest, or situated near fibrous or synovial membranes, where, instead of weakening the textures, abscesses frequently have the contrary effect, by thickening the periosteum (the covering of bone), the pleura (the lining of the chest and the covering of the lungs), the peritoneum (the covering of the bowels), and the fibrous and synovial structures.