A Study of the Virulence of Meningococci for Man and of Human Susceptibility to Meningococcic Infection

Epidemic cerebrospinal meningitis presents a number of immunological and epidemiological problems. Chief among these are the rôle of the meningococcus carrier in the dissemination of the infection and the factors that make him a distributor rather than a victim. Why, in an individual who develops meningitis, do the meningococci invade the deep tissues, and in the carrier confine themselves to the surface of the mucous membrane? Morphologically and culturally the cocci from the two sources are identical; both series are capable of setting up infection in susceptible men and animals; both are agglutinated by polyvalent, antimeningococcic serum. In searching for an explanation, two phenomena must be considered. One is the virulence of the meningococci for human beings; and the other is the susceptibility of human beings to the attacks of meningococci. It is important to recognize that these are two separate and distinct phenomena—that the distinction is not one of phrasing, only. We have not to do, as in the case of resistance and susceptibility, with two sides of the one shield—with a single problem positively or negatively stated—but with two different problems. The one concerns a variable x, relative to a constant y; the other concerns a variable y, relative to a constant x. In final result, increasing either of these factors may, indeed, be equivalent to decreasing the other; but the process—the mechanism—is different. And it is the latter we have to study.