1. A lytic agent was not demonstrable in culture filtrates of either the parent or variant type of the scours organism.
2. The parent type was resistant to the action of a "weak" bacteriophage, obtained from the animal host, while the variant type was susceptible.
3. Exposure of the variant type to the scours bacteriophage was attended by agglutination of the cells, marked swelling, and an alteration of the contents prior to lysis.
4. The manifestations of variation which regularly occur on agar plate cultures of the scours organism do not appear to be the result of bacteriophagic stimulation.