in medicine, a white or yellowish matter designed by nature for the healing and cementing of wounds and sores.

The origin and formation of pus is as much unknown as that of any other animal fluid. In an inaugural dissertation published at Edinburgh by Dr Hendy, the author supposes pus to be a secreted fluid. It has been thought by many, that pus is either a sediment from serum when beginning to putrefy, or that it is the same fluid infipitated by the heat of the body. But both these opinions are refuted by some experiments of our author, which show, that pus is much less inclined to putrefaction than serum, and the putrefaction of both is hastened by an addition of some of the red part of the blood. Some other experiments were made in order to try whether pus could be artificially produced. A thin piece of lamb’s flesh, applied to an ulcer discharging laudable pus, and covered over with lead, did not assume the appearance of pus, but became fetid, and was much lessened. Serum, in its inflammatory and in its ordinary state, and lymph in different states, were applied to the same ulcer, which still discharged good pus; but none of these were converted into pus; on the contrary, they became very putrid.

In opposition to these arguments of our author, however, it may be alleged, that if pus was a secreted fluid, the vessels by which it was secreted would certainly be visible; but no such thing has ever been observed: on the contrary, it is certain that pus cannot be formed unless the air is excluded from the wound. These disputes, however, are of no great consequence: but in some cases it becomes a matter of real importance to distinguish pus from mucus; as thus we may be enabled to know whether a cough is consumptive, or merely catarrhous. See Mucus. Mr Home, in a dissertation on the properties of pus, in which he avails himself of the experiments of Mr Hunter, as delivered in his Physiological Lectures, says, “that the characteristic of pus is its being composed of globules; and he thinks that the presence of globules seems to depend upon the pus being in a perfect state. It differs from the blood in the colour of the globules; in their not being soluble in water, which those of the blood are; and from the fluid in which they swim being coagulable by a solution of sal ammoniac, which serum is not.” Reflecting the formation of pus, our author adopts the idea suggested by Mr Hunter, that the vessels of the part assume the nature of a gland, and secrete a fluid which becomes pus. Mr Home ascertains, by experiment, that pus, at its formation, is not globular, but a transparent fluid, of a consistence, in some sort, resembling jelly; and that the globules are formed while lying upon the surface of the sore; requiring, in some instances, while the influence of the external air is excluded, fifteen minutes for that purpose.