The reaction of the peritoneum to trauma and the resistance of the peritoneum to bacterial invasion have always been subjects for study and speculation. Notwithstanding the countless investigations and clinical observations of past years, there is yet much to be learned. It is generally understood that aseptic trauma to the peritoneum gives rise to a reaction tending to produce healing with the formation of adhesions of scar tissue of greater or less degree. If in addition to trauma there is bacterial contamination of the peritoneum, the healing process is complicated by infection or peritonitis. In the broadest sense, the term peritonitis may include the reaction of the peritoneum to any injury, whether it be simple trauma, chemical irritation or infection. That mere contamination of the normal peritoneum with living pathogenic bacteria does not necessarily produce fatal peritonitis is a matter of common knowledge. Dogs often will tolerate massive intraperitoneal injection