1. Each bacteriophage is a specific antigen.
2. The antibodies against the bacteriophage are independent of those against the bacterial substrate used in preparing the phage.
3. The reaction of neutralization is closely analogous to that of the neutralization of toxin by antitoxin.
4. The serum of mice experimentally infected with mouse typhoid (M.T.) did not become capable of neutralizing phages acting on the infecting organism.
5. The use of the reaction of neutralization of bacteriophage in the diagnosis of disease as proposed by Sonnenschein seems impractical.