Succinic acid is a major end product of two cellulose-fermenting bacteria isolated in pure culture from the rumen of cattle and sheep. Ruminococcus flavefaciens, isolated by Sijpesteijn (1948, 1949, 1951), produced some 0-5 m-mole succinic acid per m-mole cellulose (calculated as glucose) fermented. Bacteroides succinogenes, isolated from the bovine rumen by Hungate (1950), was found by this au...