1. Methane was produced in vitro by incubating cell suspensions of rumen bacteria with glucose, under nitrogen. The amount of methane produced varied considerably and was lowered by high glucose concentrations. Carbon dioxide, acetic acid, propionic acid, butyric acid and lactic acid were also produced. An oxidation–reduction balance of near unity could be calculated, although carbon recovery was low. Under the experimental conditions, rumen bacteria used most of the metabolic hydrogen produced during the oxidation of glucose to form lactic acid. 2. Lower methane production at high glucose concentrations was balanced by higher lactic acid production. Low pH values due to a high production rate of lactic acid might explain the inhibition of methane production. 3. No lactic acid, less methane, but considerably more propionic acid were formed when nitrogen was replaced by carbon dioxide in the incubation system.
