1. Streptococci injected into the circulation of cats are quickly withdrawn and are found most numerously in the lung, less numerously in the liver and spleen, and in small numbers in the bone marrow, lymph nodes, muscle, and kidney.
2. The streptococci taken up by the lung are killed within 5 to 8 hours, although they remain visible in films for a number of days. In the liver they are killed less rapidly, and in the spleen a few may remain viable for a considerable period.
3. This bactericidal action may be demonstrated in pieces of excised lung but not in lung extracts, and is apparently dependent on the action of the living cell.
4. Streptococci injected into a susceptible animal, the rabbit, are also promptly removed from the circulation, but are distributed in different proportions, the liver and spleen absorbing almost as many as the lung, and the muscles also taking up an appreciable number.
5. As in the cat, the organisms taken up by the lung and liver of the living rabbit are promptly killed. Those which lodge in the muscles, however, multiply rapidly.
6. About the time that the streptococci have begun to develop in the muscles (4 to 8 hours after injection) the number in the blood stream begins to increase.
7. The increase in the blood stream is not due to exhaustion of the mechanism of their removal nor have these organisms acquired a resistance sufficient to maintain them in the blood stream of a normal animal. The septicemia, then, is probably the resuit of washing out of organisms from the infected tissues.
8. Attempts to immunize rabbits have been unsuccessful, but in certain treated animals the distribution of the organisms among the various organs approached that found in insusceptible animals; i.e., cats.