A Further Contribution to the Knowledge of the Opsonins

1. The determination of Wright's index of the opsonic content of the blood and other fluids of the body is open to serious and in part unavoidable errors and should be abandoned in its present form. 2. Conclusions based upon the determination of the opsonic content of the blood, according to Wright's method, are accordingly not uniformly reliable. 3. The percentage index is a valuable check on Wright's bacillary index, but likewise does not furnish an adequate idea of the opsonic content of the blood, unless carried out with progressive dilutions to the point of opsonic extinction. 4. The opsonins of normal blood serum are not specific. 5. The specificity of the opsonins in "immune" sera has not been satisfactorily established, but appears probable. 6. An opsonic immunity, in the sense of a continued high opsonic content of the blood does not exist. 7. In the blood and exudates of infected individuals substances may be present which exercise an inhibitory effect upon phagocytosis.