Although specific antibody and complement have long been known to produce appreciable bactericidal effects on Gram-negative organisms, in vitro, the role of this phenomenon in immunity to infections with these organisms is still not clear (1). Similarly, certain antibiotics, including chloramphenicol, produce significant inhibition of the growth of Gram-negative bacteria in the test tube, and, in favorable instances, also exert a chemotherapeutic effect on infections such as typhoid fever. The quantitative correlations between these two actions of the drug are, however, not entirely defined nor is it known in satisfactory detail whether, in addition to the drug, immunity factors such as antibody, complement, and phagocytes play a significant part in recovery.In a recent investigation (2) it has been possible to determine with some precision the quantitative relations among antibody, complement, and bacteria which affect the bactericidal reaction. In a separate series of investigations in our laboratory, attention has been directed to the development of more precise methods of determining the susceptibility of bacteria to antibiotics, and to the interpretation of the data in terms of modes of action, at least on a populational level (3).The convergence of these two lines of investigations has now permitted the establishment of a model in vitro system for the quantitative study of some of these therapeutic factors, and their interactions, with a greater precision than has been available with the methods used hitherto. Although important new information can be obtained, the approach is still inadequate so long as factors such as the participation of phagocytic cells are neglected. It is hoped, however, that the latter, in particular, may be included in a proposed extension of our procedures.
