The Somatic Agglutinin and Immunity in Mouse Typhoid *

That the degree of immunity to B. enteritidis infection induced by enteritidis (acetone-killed and heat-killed) and by typhoid (acetone-killed) vaccines does not correlate with the content of the O agglutinin to appear in the sera of the immunized groups has been reported3. It was further shown that although both types of the enteritidis vaccine excited the formation of 0 agglutinins to nearly the same extent, the immunity produced by immunization was greater following use of the acetone-killed agent. B. typhosus vaccine also produced 0 agglutinins without affording any appreciable immunity to the enteritidis infection. These observations suggest that the rOle played by the 0 agglutinin in immunity can hardly be that of an essential element. The mere fact that this agglutinin may be present in groups of animals which have been subjected to immunizing treatment, with one group showing protection and the other lacking it entirely certainly minimizes the importance of this O antibody, or suggests that immunity response is based upon principles other than the agglutinin. The questions involved can hardly be resolved by titrations of antibody alone, but such determinations taken in conjunction with actual tests for crossed immunity might well provide desirable information. Indeed, other workers have made such experiments on crossed immunity within the enteric group, but their results have been in some measure conflicting, either in point of fact or in interpretation.