MICROCOCCUS INTRACELLULARIS MENINGITIDIS 539 



occurrence, and since there are in every epidemic a very much larger 

 number of carriers than of cases, the carrier is the chief epi- 

 demiological problem. As far as infection of new individuals from 

 patients is concerned, experience during the New York epidemic 

 showed only two or three cases of infection of doctors and nurses, 

 although the hospitals in the city were constantly handling consider- 

 able numbers of the sick. In our epidemiological experience with 

 the army, the actual tracing of one case to a preceding one was 

 also relatively very rare. This does not mean that the greatest 

 precautions should not be taken to prevent such transmission in 

 hospitals and sick room. But the epidemiological emphasis lies with 

 the carrier. 



This rareness of transmission from cases to the healthy is in 

 our opinion due to the peculiar conditions of susceptibility that pre- 

 vail in relation to meningitis, and the fact that the number of 

 people with whom the sick come in contact is relatively small. 



The susceptibility of man to meningitis is a curious one, different 

 in some aspects from susceptibility relations to almost all other 

 infections, except perhaps poliomyelitis. In the general population 

 there seems to be a great variability in individual susceptibility to 

 infection with the meningococcus, a variation which can be traced 

 to no determinable cause. Unlike pneumonia, temporary fluctua- 

 tions in well being, produced by respiratory disease, malnutrition, 

 exposure to cold, etc., do not seem to play a determining role. The 

 disease indiscriminately picks out individuals here and there, some 

 of them in the most robust health, strong and hardy, while sparing 

 associates who may be feeble and run down. It is obvious that some 

 individuals are normally resistant and will not come down, in spite 

 of considerable exposure, while others are delicately susceptible. 

 The difference may possibly have been produced fortuitously by the 

 fact that some individuals may have been carriers at one time or 

 another, and have become, thereby, spontaneously immunized. It 

 is difficult to get at this question experimentally, and there are no 

 serum or other reactions which we can apply at the present time, 

 by which we can discriminate between the susceptible and the non- 

 susceptible of a community. There is no available method, more- 

 over, by which we can distinguish between virulent and non- virulent 

 strains of meningococci. 



The Carrier Problem. As stated above, the meningococcus car- 

 rier probably is the source of infection in most of the cases that 



