FIG. 3.

Bacteremia, expressed as number of CFU per milliliter of blood from individual mice after intraperitoneal challenge with 10 times the LD₅₀ of live virulent pneumococci type 4 (∼20 CFU/mouse). Groups of mice were immunized intranasally either with whole heat-inactivated pneumococci type 4 mixed with CT (solid diamonds) or with the same antigen without CT (solid circles) or were not immunized (open circles). The dotted line indicates the limit of detection of bacteremia. The mice were challenged 1 week after the fourth nasal immunization dose, which corresponds to day 28 in Fig. 2.