Humoral antibodies play a critical role in preventing systemic meningococcal disease. The study shows that individuals susceptible to meningococcal disease lack humoral antibodies to meningococci. This is supported by epidemiological findings, such as the high incidence of meningococcal disease in infants and the cyclical nature of outbreaks. The study also found that convalescent sera from patients with meningococcal disease have high levels of antibodies that can kill meningococci. However, sera from patients with meningococcal disease lack bactericidal activity against the homologous strain. This suggests that the lack of humoral antibodies is a key factor in susceptibility to meningococcal disease. The study also found that individuals who lack bactericidal antibodies to meningococci are more likely to become infected. The study was conducted during an outbreak of meningococcal disease among military recruits. The results showed that 54 out of 492 recruits lacked bactericidal activity against the prevalent disease-producing strains. Of these, 44 acquired a meningococcus during the 8 weeks of training, but only 13 were compatible with the case strains. Of the 13 exposed susceptibles, 5 developed systemic meningococcal disease—an incidence of 38.5% of susceptibles, but only 1% of the total population. These findings indicate that the majority of susceptible individuals escaped clinical infection because they were not exposed to the prevalent strains of pathogenic meningococci. The study also found that the incidence of disease was primarily associated with the incidence of exposure of susceptibles to the pathogenic strains. While 81.5% of the presumed susceptibles acquired a meningococcal strain, only 24.1% acquired an organism similar to the prevalent disease-producing strains. Of the exposed susceptibles, 38.5% developed systemic meningococcal disease. The study concludes that susceptibility to systemic meningococcal disease is related to a selective deficiency of humoral antibodies to pathogenic strains of meningococci.Humoral antibodies play a critical role in preventing systemic meningococcal disease. The study shows that individuals susceptible to meningococcal disease lack humoral antibodies to meningococci. This is supported by epidemiological findings, such as the high incidence of meningococcal disease in infants and the cyclical nature of outbreaks. The study also found that convalescent sera from patients with meningococcal disease have high levels of antibodies that can kill meningococci. However, sera from patients with meningococcal disease lack bactericidal activity against the homologous strain. This suggests that the lack of humoral antibodies is a key factor in susceptibility to meningococcal disease. The study also found that individuals who lack bactericidal antibodies to meningococci are more likely to become infected. The study was conducted during an outbreak of meningococcal disease among military recruits. The results showed that 54 out of 492 recruits lacked bactericidal activity against the prevalent disease-producing strains. Of these, 44 acquired a meningococcus during the 8 weeks of training, but only 13 were compatible with the case strains. Of the 13 exposed susceptibles, 5 developed systemic meningococcal disease—an incidence of 38.5% of susceptibles, but only 1% of the total population. These findings indicate that the majority of susceptible individuals escaped clinical infection because they were not exposed to the prevalent strains of pathogenic meningococci. The study also found that the incidence of disease was primarily associated with the incidence of exposure of susceptibles to the pathogenic strains. While 81.5% of the presumed susceptibles acquired a meningococcal strain, only 24.1% acquired an organism similar to the prevalent disease-producing strains. Of the exposed susceptibles, 38.5% developed systemic meningococcal disease. The study concludes that susceptibility to systemic meningococcal disease is related to a selective deficiency of humoral antibodies to pathogenic strains of meningococci.