Pneumococcal otitis media was experimentally induced in guinea pigs to examine the tissue responses of the middle ear to the types and doses of S. pneumococcus. Type 3, group 19 and group 23 were used. The bacterial cell count was adjusted to 103/ml-106/ml, and 100μl were inoculated into the middle ear cavity. Type 3 caused severe inflammation by challenge of several tens of cell count. Even after 3 weeks, the middle ear discharged a turbid or purulent exudate from which the bacterium was detected. Groups 19 and 23 caused approximately the same degree of inflammation by inoculation of several hundreds of cell count. However, when the cell count was below 103/ml, only almost normal or serous excretion was slightly discharged from the middle ear.
