1. Pneumococcus vaccine was administered to 29 patients with pneumonia to determine whether a state of immunity could be induced during the course of the disease. Twenty patients received an intravenous injection of pneumococcus vaccine or pneumococcus filtrate. Nine pneumonia patients received an intradermal injection of vaccine. Eight patients with miscellaneous disease received an intravenous or intradermal injection of pneumococcus vaccine.
2. Of 23 tests in which the serum of the patient was studied for the appearance of protective substance after intravenous injection of heterologous pneumococcus vaccine, 20 or 87 per cent showed a positive response within 6 days after the administration of the antigen. The average day of onset was 4.4 days after injection.
3. Of 9 tests of the same character following the intravenous injection of pneumococcus filtrate, 8 or 89 per cent showed a positive response. The average day of onset of protective substance was 5.6 days after injection.
4. The appearance of specific protective substance following heterologous injection of pneumococcus vaccine appeared to be due to the introduction of the vaccine and not to the natural course of the disease, as was shown by negative control experiments.
5. Of 24 tests with intradermal injection of vaccine, 10 or 42 per cent developed slight protective substance of irregular degree 4.5 days after injection.
6. No immediate reactions were observed following the intravenous or intradermal injection of pneumococcus vaccine. One chill occurred after injection of pneumococcus filtrate. Of 20 cases with intravenous injection of pneumococcus vaccine or filtrate, 2 died of their disease, one a case in which homologous vaccine was used and one in which heterologous vaccine was administered.
7. Conclusions concerning the therapeutic value of the introduction of pneumococcus vaccine in pneumonia must await further investigation. These studies demonstrate that specific protective substances generally appear 4 to 5 days after intravenous injection of pneumococcus vaccine during the course of lobar or bronchopneumonia.