In many cases the necrosis limits itself at once, the agent which produced it having acted once for all. It only remains to dispose of the dead structures. In other cases the limitation does not take place so directly, and the formation of a line of demarcation is anxiously looked for. This is frequently the case in traumatic necrosis where it may for some time be doubtful to what extent the tissues have been injured beyond recovery. The co-existence of inflammation, especially when this is associated with decomposition, often renders the limitation of the necrosis more difficult. In infective processes also, such as tuberculosis, the necrosis follows the advance of the lesion. Again in senile gangrene where the arteries are seriously obstructed, the starting point of the necrosis may be a trivial injury, and its progressive extension may go on without any signs of limitation for a considerable time.

In the disposal of the dead tissue inflammation plays a most important part. We have seen that violent inflammation is often produced by the same cause as the necrosis, or may supervene on it. This will mostly be the case in external parts where decomposition occurs. The inflammation is characterized by hyperemia and exudation, and •commonly goes on to suppuration. A layer of pus comes thus to divide the dead tissue from the living, and the dead is cast off as a slough. There remains a suppurating wound or ulcer.

In internal parts, if the necrosis be accompanied or followed by the production of irritating chemical substances, then a violent inflammation will be produced around. It is so in the case of pysemia, where there is septic embolism. In this case the inflammation will usually be violent enough to produce suppuration, and the result will be the formation of an abscess.

In the case of internal parts where there is no disturbing decomposition, or in external parts which are protected from septic contamination, the inflammation is of a much milder character. The necrosed portion now comes to act as a foreign body or dead piece of tissue; and is subject to the changes already described at p. 128. The dead tissue is often eaten into and replaced by vascular granulations, which finally contract and leave a small residue of connective tissue; or the dead piece is encapsuled and may lie quiescent. Not infrequently the encapsuled tissue undergoes infiltration with lime salts, as we shall see afterwards. In the case of necrosis in bone the external capsule is frequently composed of new-formed bone.

Literature

Carswell, Elementary forms of disease, Art. Mortification, 1834;. Virchow, Handb. d. spec. Path., vol. i.; Paget, Lect. on surg. path., p. 340; Cohn-heim, Allg. Path., vol. i., p. 52G, and Die embol. Proc.; Recklinghausen, Allg. Path.; Litten, Zeitsch. f. klin. Med., vol. i.; Koch, Traumatic infective diseases (Syd. Soc. transl.); Burdon Sanderson, Path. Trans., xxiii., Brit. Med. Jour... 1877; Weigert (Coagulation-necrosis), Virch. Arch., lxxix., p. 89; Chauveau,. Nekrobiose et Gangrene, Bullet, de l'Acad. de Med., 1873.