1. The subcutaneous inoculation of monkeys with three large doses of Pneumococcus Type I vaccine confers on them a complete immunity against experimental Pneumococcus Type I pneumonia.
2. The intravenous inoculation of small doses of Pneumococcus Type I vaccine also confers complete immunity against the homologous type of pneumonia.
3. Specific protective bodies may or may not be present in the serum of monkeys vaccinated against Pneumococcus Type I. There appears to be no intimate relation between active immunity against pneumonia and the presence or absence of protective substances in the serum of the vaccinated animal.