As already indicated, this condition is nearly always a result of inflammation in the peripheral parts from which the vessels come to the gland. The enlarged and inflamed gland is called a Bubo. The most serious of the acute inflammations are connected with infective processes, as in the case of dissecting wounds, erysipelas, phlegmonous inflammations, diphtheria, scarlet fever, splenic fever, and the plague (Bubonic plague).

The inflamed gland is enlarged, its vessels hypersemic, and the tissue softened. The enlargement is due to a great increase of lymphoid cells which accumulate largely in the sinuses. The stellate cells forming the reticulum of the sinus also swell, and their nuclei divide. The sources of the added lymphoid cells are several. They arise by division of the existing cells of the gland, as evidenced by the observation of karyo-mitosis in these cells; but they have their origin in part in the emigration of white corpuscles from the blood-vessels in the gland, and further, the primary inflammation of the periphery may send its contingent. The inflammation may subside and the gland return to its normal condition; the new-formed cells may possibly pass on into the efferent vessel and be disposed of in the circulation.

Not infrequently suppuration occurs; the tissue of the gland breaks-down and an abscess is the result. We have thus a Suppurating bubo. The inflammation usually extends to the capsule and surrounding tissue, which become involved in the suppuration. In this way the abscess advances, and the pus is finally discharged at the surface. It is a common occurrence for such abscesses to discharge on the surface of the body, but they may burst into bronchi, into serous cavities, etc. Some of these severe inflammations have a haemorrhagic and even a necrotic or gangrenous character.