Kaplan-Meyer survival curve of mice infected with type 4 S. pneumoniae. Five groups of MF1 mice (n = 6–10) were infected by the i.c. subarachnoidal route with different doses of type 4 S. pneumoniae ranging from 10 to 105 CFU per mouse. Mice were monitored for 10 days and survival was recorded. Results are expressed as percentage of survival over time.