The existing methods for diagnosis of various conditions affecting the peritoneum have not been uniformly satisfactory. The deficiency in the exact procedures has been felt especially in certain situations such as the recognition and differentiation of primary and secondary peritonitis in children, the determination of the bacterial species in the primary type and the separation of irritative from infectious conditions of the peritoneum. Even less adequate are the available means of establishing prognosis of a phase of peritonitis. The degree of bacterial activity within the peritoneal cavity, especially in the earlier stages of an infection, does not produce clinical manifestations comparable to the potential damage of which the bacteria are capable. The sudden transformation of a patient's condition from a relatively benign to a critical state is by no means as unexpected as the outward manifestations would indicate. The major activities of the bacteria occur within the confines of the