1. When the soluble specific substance of Type II pneumococcus was fed to rats, little or no increased resistance to the organism was obtained.
2. When the specific substance of Type III pneumococcus was fed, an increased resistance to the virulent organism resulted. The percentage of animals protected is smaller than when the whole or the dissolved cell is fed.
3. When the specific polysaccharide of Type I was fed, no immunity against Type II or III was obtained, and the ingestion of the specific substances of Types II and III did not protect rats against the Type I organism.