1. Feeding heat killed pneumococci grown in milk produces a fair degree of immunity.

2. Feeding acid killed degraded aruvilent organisms produces little protection.

3. Feeding the desiccated, mechanically disrupted organisms creates a high degree of protection.

4. Feeding the Berkefeld filtrate of sodium glycocholate dissolved cells produce a high degree of immunity.

5. A single ingestion of this material equivalent to between 1 and 5 cc. growth is sufficient to protect a rat against 1000 to 10,000 fatal doses. Among rats fed the equivalent of 0.1 cc. an occasional one survives.

6. This degree of protection is present 48 hours after the feeding, and to a smaller extent exists in occasional animals at the end of 24 hours.

7. The treated animals are resistant to subcutaneous as well as intraperitoneal injections.

8. A single ingestion of hydrochloric acid killed pneumococci equivalent to between 1 and 5 cc. growth also protects within 48 hours against 1000 to 10,000 fatal doses intraperitoneally injected.

9. Reference is made to results obtained in preliminary experiments with human beings.

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