Inflammation of the Peritoneum may be either acute or chronic. The Peritoneum is the great membrane which lines the cavity of the abdomen, and which partially or wholly covers the various viscera. The membrane when healthy does not show any great disposition to become inflamed, but in most cases there is reason to believe that some predisposition existed, or there was some previous unhealthy state of the membrane itself, or of the circulating blood.

It often prevails epidemically, ( as in Puerperal Fever), or it is produced by mechanical injuries of the abdomen, or by some exposure to cold, and especially to cold combined with moisture.

Sir Thomas Watson says: "Formerly, any necessary wounding of the peritoneum was thought to be attended with hazard. It was indeed notorious, that it might generally be pierced with impunity by a trocar in the operation called tapping. Operations for the relief of strangulated hernia are often followed by Peritonitis; but other and graver causes than the knife of the surgeon are then at work. Especially was the free access of air to the general membrane dreaded as being highly dangerous. But what happens in cases of ovariotomy is sufficient to show that the peritoneum may be largely exposed to the atmosphere, may be smeared with blood, mucus, and the products of ovarian disease, may be sponged clean, after the operation, as freely as, and much more thoroughly than one would sponge the abdominal cavity in a dead body, without any resulting inflammation. This is now a matter of every day experience. A relation of mine was the subject of ovarian dropsy, for which she was tapped. Shortly afterwards the puncture in the dropsical ovary re-opened, and fluid escaped into the general cavity of the peritoneum. Thereupon the diseased ovary was extracted by Mr. Spencer Wells, in the presence of Dr. Arthur Farre. I have been informed by these gentlemen that the whole of the peritoneal surface presented a uniform blush of redness, marking, it may be presumed, that stage of congestion which is just short of actual inflammation. This lady recovered without a single untoward symptom, and has since again become the mother of children."

Acute inflammation of the peritoneum is characterized by pain in the abdomen, increased on pressure, and attended with fever. We know that it is not inflammation of the liver, for there is no pain in the right side of the body in particular, increased by lying on either side, no pain in the shoulder, no jaundice, no vomiting perhaps; neither is it inflammation of the bowels or stomach, for there is no disturbed function of the alimentary canal to denote such inflammation.

The pain is increased when the patient sits up; also by drawing a long breath, by coughing, sneezing, or straining. Though the pain is, at first, sometimes confined to particular spots, yet generally it soon extends over the whole abdomen. But before the inflammation has become universal, while it is yet restricted to particular spots, the pain is often much increased by pressure made on other parts of the abdomen. The patient cannot sit up, nor usually lie on his side; but remains always upon his back, with his legs drawn up, and, in order to avoid pain, he gets into a way of breathing by means of his ribs only. The breathing is therefore both frequent and shallow; there are perhaps forty, or even sixty respirations in a minute, instead of eighteen or twenty. When we find a person lying only on the back, with the knees up, breathing in this manner, and complaining of tenderness of the belly on pressure, and feverish withal, we may be tolerably sure, (unless that person be a hysterical girl), that the peritoneum is inflamed, whatever else may be the matter.

The pain in Peritonitis is generally sharp, cutting, or pricking in its character. And, independently of any pressure made from without, or caused by any change of posture, this pain is apt to be much aggravated at intervals. This, when the inflammation is general, is sometimes owing to the passage of wind along the bowel, partially distending it, and stretching the inflamed membrane.