The term abscess denotes a collection of pus in the substance of the tissues, surrounded by a wall of lymph. The formation of the acute form is as follows: The exciting cause, acting as an irritant, induces an afflux of blood to the centre of the affection, and the distended capillaries pour out liquid exudation, which coagulates at this centre into plastic lymph, expanding the meshes of the neighboring surrounding tissues with a more serous fluid.

Leucocytes are formed from cell proliferation in the plastic lymph; but, on account of their not being in a proper place for their growth and development into tissue, they become changed into pus, which collects in a cavity formed by it, and the result is an abscess. As these phenomena occur in rather quick succession, pain, heat, redness and swelling are present, and also constitutional disturbance in the form of hectic fever.

The increase of an abscess in size is attended with a certain amount of redness on the surface over it and to which it is approaching, this increasing redness being preceded by more or less oedema of the tissue beneath, which is owing to the protruding of the serous exudation surrounding the central collection of pus. The centre of the surface redness then presents a more prominent and elevated point, where the outer tissue becomes thinner, purplish, or livid, and soon the yellow pus within is visible through it - a condition to which the term pointing is applied. Soon after the "pointing," the integument gives way, and the pus exudes through the opening thus made.

This thinning and weakening of the surface is caused by the stretching and obstruction of the blood vessels, which convey the nutritive supply from beneath, by the pressure of the enlarging abscess to such a degree that the surface integument is deprived of its blood and slowly dies by minute particles, the dead material being added to the contents of the abscess.

An abscess unattended with such symptoms as pain, heat, and redness, is termed a cold abscess, and its presence depends upon a low degree of vitality. Such an abscess presents the same phenomena of pus formation as the acute form, but resembles more the growth of a tumor, as all the symptoms may be absent except the swelling. The formation of pus on the surface of a tissue, such as mucous membrane, is not so serious as that in an abscess, as the conversion of the leucocytes into pus requires but little more increased activity than in cell germination. The exudation takes place from the network of capillaries which exist beneath every mucous membrane, and which furnishes nourishment for the constant renewal of the epithelium, and any injury received causes a fluxion of blood to the capillaries, which increases the cell proliferation. The effect is, then, to promote an increased discharge from the surface of the membrane, in the form of pus. Suppuration from mucous membrane usually causes pain, heat, imcreased redness, and swelling of the inflamed surface, owing to the exudation into the meshes of the connective tissue beneath, and recovery is characterized by diminished fluxion of blood to the affected part, and consequent lessening of cell production; the cells resume their function of producing epithelial tissue, the pus becomes thin and more fluid, and finally ceases when the normal conditions again appear.

Hectic fever is a symptom of destructive inflammation, and is a persistent, low form of continued fever, characterized by remission and exacerbation morning and night. This form of fever is caused by absorption into the blood of some of the products of inflammation, in such quantities and so gradually as not to produce an immediate fatal result, and inducing a regular succession of chill, fever, and perspiration during the space of every twenty-four hours. Its effect is progressive emaciation and a tendency to fatal termination, if the cause is not removed, through combustion of tissue material to supply the fever heat. The regularity of the night sweats, and the pulse retaining its frequency during the apyrexia, even in the morning, when the temperature is normal, are the diagnostic signs of hectic from typhoid and malarial fevers.

The most unfavorable symptoms of hectic fever are the higher fever in the evening, the increase in the frequency of the pulse, the more exhausting night sweats, with the occurrence of aphthae in the mouth, and diarrhoea.