1. Guinea pigs can be rendered hypersensitive to tuberculo-protein by small, repeated, intradermal injections of active tuberculo-protein.

2. The addition of tuberculo-phosphatide to the protein speeds up the process of sensitization and enhances it so that the reactions become indurated and necrotic, closely simulating those of the disease.

3. Active tuberculo-proteins induce a new formation of monocytes and some epithelioid cells. The addition of phosphatide to the protein brings about a massive formation of epithelioid cells.

4. With the increased cellular reaction to the mixed injections may be correlated the increase in the speed and intensity of the sensitization.

5. The intradermal route is the best for these sensitizations, probably because it provides the greatest dose per cell of the sensitizing agent.

6. The degree of sensitization artificially obtainable by the synergistic action of tuberculo-phosphatide and tuberculo-protein is quite comparable to the degree of sensitization naturally occurring in tuberculous animals; moreover, this degree of sensitization may be induced with amounts of the materials from the bacilli which could conceivably be present in the tissues of an infected host.

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