1. The rate of inactivation of an anti-coli phage by filtrates of cultures of the homologous bacteria has been studied.
2. The inactivation rate at 37°C. is proportional to phage concentration and filtrate concentration.
3. At 0°C. the rate of phage inactivation becomes proportional to the square root of the filtrate concentration.
4. A reaction scheme to account for these observations is suggested and discussed.
5. This coli-phage is also inactivated by relatively large concentrations of soluble starch, inulin, gum arabic, and acetylated gum arabic.
6. The inactivation is markedly influenced by salt concentration, being rapid at moderate salt concentrations and slow at high or extremely low salt concentrations.
7. The inactivated phage cannot be regenerated by high salt concentrations, or by soaps.