The bactericidal activity of phagocytin on Gram-negative enteric bacilli is influenced by the reaction of the medium; the more acid the environment, the more marked is the activity.

Phagocytin exerts approximately the same action whether citrate, acetate, or phosphate salts are used as buffer, and the addition of glucose, casein hydrolysate, or cation binding agents does not produce notable change. Although proteins in general have but little effect, the inclusion in the medium of a high concentration of bovine plasma albumin neutralizes the lethal action of phagocytin on enteric bacilli. Very high concentrations of magnesium or calcium ions antagonize but do not completely block the bactericidal effect.

The bactericidal activity of phagocytin is essentially independent of the numbers of bacteria exposed; a 100-fold increase m the numbers of enteric bacilli results in approximately a 2-fold increase in the concentration of phagocytin required to kill 90 per cent of them.

When susceptible microorganisms are exposed to phagocytin at 0°C., practically no killing takes place. At higher temperatures the bactericidal action is rapid, being well advanced in 5 minutes and complete within 30 minutes.

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