This disease is due to the existence of the tubercular virus in the peritoneal cavity. The virus seldom gets into the sac from tubercular ulcers of the intestine, apparently because the intestinal lymphatics are subperitoneal and do not connect with the interior of the sac. Tuberculosis of the lymphatic glands, more especially those of the mesentery, seems to be the principal primary source of tuberculosis of the peritoneum. An old caseous gland may break down and rupture into the sac, and this may occur although the glands may be only to a slight degree affected. Tuberculosis of the vertebrae may give rise to it, and in some cases tuberculosis of the testicle and vas deferens has extended to the peritoneum, the disease being in that case concentrated in the inguinal region where the vas deferens approaches nearest to the peritoneum.

Having reached the peritoneum the virus is carried hither and thither throughout the sac by the regular currents. The consequence is the formation of innumerable tubercular nodules and an Inflammation of the peritoneum. The inflammation is at first acute, accompanied by serous and, usually, fibrinous exudation as in septic inflammations. There is thus often considerable swelling of the abdomen. In some cases the inflammation is unusually acute and it may even be suppurative in character.

By the time the case comes to be examined post mortem the acute stage has usually passed off and we find evidences of chronic inflammation in the form of thickening of the peritoneum and multiple vascularized adhesions in every part. The loops of the intestine are adherent to each other, and the superficial ones to the anterior wall of the abdomen, the omentum is adherent to the intestine, the liver to the diaphragm, and so on. In fact the peritoneal cavity is obliterated by adhesions. In the midst of these adhesions are numerous yellow masses of very various sizes, some as large as split-peas, and usually flat. These caseous masses are composed of groups of tubercles which have very much the character of those found in tubercular pericarditis. The caseous tubercles have developed in the usual way out of grey miliary tubercles, and examination will usually show examples in the various intermediate stages.

The condition of the Omentum is worthy of special mention. It is drawn together and thickened, and closely adherent to the intestine and wall of the abdomen, while in its substance numerous tubercular masses are to be found. *

It has already been mentioned that Tubercular pleurisy often develops in association with tubercular peritonitis. There is in the pleura for the most part a serous and sometimes a fibrinous exudation, and as the eruption is usually recent the tubercles are in the form of small white or grey nodules. They are commonly grouped mainly in the lower part of the pleural cavity, in this way indicating the source of the infection.

Healing is not infrequent in tubercular peritonitis, but the resulting conditions are rarely the subject of observation. The author had the opportunity of examining a case ten years after the patient had passed through an attack which was diagnosed as tubercular peritonitis. The peritoneum was obliterated by soft connective tissue adhesions, which united the intestines and the various organs together. There were no tubercles visible, but here and there a small cretaceous mass in the midst of the adhesions. When the tuberculosis had been overcome the dead caseous matter had remained. This was in great part absorbed as dead animal matter. Where, from the size of the mass or otherwise, absorption did not occur, calcareous infiltration took place. The adhesion of the peritoneum may be more localized, and by the stretching of the adhesions, bands or bridles may be formed under which the intestine may be incarcerated. The author has observed several cases of this kind.

In Acute miliary tuberculosis, the appearances are altogether different to those of tubercular peritonitis. The tubercles are very-small grey nodules hardly visible to the naked eye and specially abundant in the upper part of the abdomen and in the omentum. They are in connection with the blood-vessels and not on the surface of the membrane, being really subperitoneal, and there is no inflammation.