Heterologous Immunity Reactions Between B. Typhosus and B. Enteritidis *

Immunity has been considered one of the most specific of biologic reactions and it has been assumed that an infection induced by one organism within a closely related group does not immunize against another organism of the same group. The recent studies of Weil, Felix, and Olitzki suggest strongly that there is a group immunity between typhoid and enteritidis infections. The results here reported are based upon experiments made in an attempt to determine whether a crossed immunity exists between B. typhosus and B. enteritidis infections. In studies bearing upon the interrelationship of immunity phenomena two methods of approach are available; first, the serological method which is designed to show certain common factors in serologic response; second, crossed protection tests, such as would demonstrate an actual increased resistance to infection. Needless to say, the first of these methods has very largely been the method of choice, solely because of its relative simplicity and despite the fact that for a long time the validity of conclusions based upon this method has been subject to more or less criticism. In the studies here reported both of these methods have been applied. The first part of the paper deals with serology, and the agglutination reactions between B. typhosus and B. enteritidis are shown. In addition, and perhaps of greater importance, are the results of the bactericidal effect of immune sera on the two organisms. The second part of the paper deals with animal protection tests. That the serological method, as applied to the problem, might serve in some measure to show the common character of the immunities induced by the two bacterial types under consideration was suggested by some of the recent reports dealing with organisms of this general class. The contributions of greatest significance are