Lytic filtrates, active against Bacillus dysenteriœ Shiga, Bacillus coli, Bacillus pestis caviœ, and staphylococcus respectively, proved to be differently affected by changes in hydrogen ion concentration.
Anti-staphylococcus lysin was the least resistant of the four, showing deterioration in 3 hours at 7°C. beyond the zone of hydrogen ion concentration limited by CH = 6.3 x 10–5 and CH = 1.6 x 10–9. Under the same conditions, the zone of resistance of anti-coli filtrate lay between CH = 2.7 x 10–3 and CH = 2.5 x 10–11, and that of anti-Shiga between CH = 1-7 x 10–4 and CH = 1-3 x 10–11. Anti-pestis caviœ filtrate was most resistant of the four, retaining its full activity in the zone from CH = 1 x 10–3 to CH = 3.5 x 10–12.
The fact that these differences in individual resistance persisted, notwithstanding the repeated passage of lytic filtrates through cultures of bacteria other than those against which they were primarily active, seems to offer evidence in favor of a multiplicity of bacteriophages.