STUDIES ON EXPERIMENTAL PNEUMONIA

1. The subcutaneous inoculation of monkeys with Pneumococcus Type I vaccine in doses comparable with those employed in man does not protect them against subsequent attacks of Pneumococcus Type I pneumonia, either spontaneous or experimental. Furthermore, the occurrence of Pneumococcus Type IV pneumonia among monkeys that have been vaccinated with Pneumococcus Type I lipovaccine indicates that the vaccinated animals develop no cross-protection against other types of pneumonia. 2. Vaccination does, however, modify the course of the disease. Invasion of the blood stream by the pneumococcus in vaccinated animals is usually slight, and the proportion of recoveries is considerably higher for vaccinated than for unvaccinated monkeys. 3. Pneumococcus saline vaccine produces a greater amount of protective substance in the serum of the vaccinated animal than does pneumococcus lipovaccine and is probably, therefore, a better antigen. Both, however, fail to protect the animal against pneumococcus pneumonia. 4. Subcutaneous vaccination with pneumococcus vaccine gives definite protection against experimental pneumococcus septicemia. In other words, vaccination may induce a humoral immunity without protecting against intratracheal infection. 5. In view of the fact that monkeys are highly susceptible to pneumococcus infection, a strict analogy cannot be drawn between pneumococcus immunity in monkeys and pneumococcus immunity in man, since in the latter a considerable amount of resistance already exists, probably by reason of repeated exposure to pneumococcus infection.