The incident energies required to kill Staphylococcus aureus or to inactivate its homologous bacteriophage have been measured at the various wave-lengths of the quartz mercury vapor arc between 238 and 302 mµ and found to run strictly parallel, the readings for the S. aureus phage being obtained at a uniformly higher energy level. This difference in levels is of less significance than the striking similarity in the shapes of the energy curves, which indicate that in both instances the same organic structures are absorbing the radiations. The results are open to three interpretations. The most obvious is that the bacteriophage is a submicroscopic organism. Again, it is possible that the bacteriophage is a product of its own lytic action on the homologous bacterium and contains the essential structural units which in S. aureus also are destroyed by ultraviolet light and thus cause the death of the organism. A third, more remote explanation is that the phage, of wholly unknown nature, is absorbed on S. aureus material in so intimate a bond that the alteration of this material by irradiation renders the phage incapable of further lytic activity.

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