Intestinal bacteria were classified as gram-positive or gram-negative by an electrode system with a basal plane pyrolytic graphite electrode and a porous nitrocellulose membrane filter to trap bacteria. When the potential of the graphite electrode was run in the range of 0 to 1.0 V versus the saturated calomel electrode (SCE), gram-positive bacteria gave peak currents at 0.65 to 0.69 V versus t...