This occurs not infrequently about the period of puberty or in connection with menstruation, but in the majority of cases it is related to lactation. In connection with lactation, and especially at its commencement, the structures in the mamma are the seat of very active processes; there is hyperemia and an active secretion of milk. Under these circumstances inflammation is more readily induced than usual, but in cases of acute, and more particularly suppurative inflammation, the actual presence of an irritant must be inferred. It may happen that contraction of the arteries from accidental circumstances, such as exposure to cold, is capable of setting up inflammation. Even a general irritation of the vaso-motor centre, when the skin is exposed to cold, may, by reflex action on the highly excited vascular system of the mamma at the commencement of lactation, strongly predispose to inflammation. The actual irritant finds access in most cases by the nipple and lactiferous ducts. In many cases it takes origin in cracks and ulcers of the nipple, the irritant which has caused the lesion in the nipple extending along the tubes and causing inflammation in the mamma. On the other hand, an infective agent may extend along the ducts from without, apart from any preceding lesion of the nipple.

The inflammation is usually an acute one, and is accompanied \>y exudation, the interstitial tissue being packed with leucocytes and the breast hardened. This hardening is often local, as the inflammation is usually to some extent limited to certain parts of the breast. Very often the exudation of leucocytes goes on to actual suppuration and the formation of Abscess, sometimes with sloughing of the tissue. The abscess so formed may have extensive ramifications in the mamma, especially if the pus does not get vent externally. After evacuation the cavity fills with granulation cells, and finally closes, and a cicatrix is formed.

A Chronic inflammation resulting, after the usual manner of interstitial inflammations, in induration of the organ, has been described, but is not of frequent occurrence.