Coincident with the marked macrophage reaction induced in the peritoneal cavity by oil injection, there is an increased resistance of this location to bacterial infections. Animals so prepared dispose of Bacillus coli in a much shorter time than normal animals, and survive multiples of the fatal doses of staphylococci and pneumococi.
The amount of oil injected is in itself incapable of inhibiting bacterial growth, nor is cell-free exudate from an oil-injected animal potent in this regard. The macrophages in the exudate, on the other hand, actively phagocytize bacteria. These facts lead to the conclusion that the increased resistance is due primarily to the action of macrophages.