The investigations of the influence of oxygen on the bacteriophage phenomenon recorded in this paper show that this factor plays an important role which is due exclusively to its ability to induce certain changes in the behavior of bacterial cells towards lytic principle. At certain H ion concentrations both aerobic and anaerobic cultures can be made resistant in the absence of lytic principle. The resistance thus acquired is of a stable nature under suitable conditions. If the lytic principle is added to aerobic or anaerobic types of resistant strains the cultures are able to regenerate it to a certain extent. However they do not undergo any visible lysis themselves even under the action of lytic principles which were passed through several generations of these types. The principles regenerated by both types of resistant cultures are identical in action with each other as well as with the stock lytic principle.
These experiments suggest a new method of investigation into the hitherto unexplained nature of resistance of bacteria towards bacteriophage.