the unequal effectiveness of immunity to these strains ( the more virulent were the strains , the more effective immunity they produced ) was due to the fact that their populations contained different amounts of organisms in phase i responsible for infective action and immunity , and also , which was heretofore unknown , for the sensitivity of these bacteria to immunological action : the greater their virulence , the greater their sensitivity .
C0029235
organisms
C0004611
bacteria