Glucose is fermented by homofermentative lactic acid bacteria with the formation of lactic acid, with essentially traces of acetic acid, carbon dioxide and glycerol; in addition to these ethyl alcohol is formed by heterofermentative forms;Physiologically the heterofermentative species of Lactobacillus are very closely related to Leuconostoc;Acetic acid and ethyl alcohol are probably formed from 3-carbon intermediaries, each accompanied by equimolar quantities of carbon dioxide;Pyruvic acid and lactic acid are discussed as probable intermediary compounds. The latter is fermented as probably acetic acid and carbon dioxide. Pyruvic acid has been isolated as an intermediary in the breakdown of lactic acid. Acetic acid, lactic acid and carbon dioxide are formed from pyruvic acid in equimolar quantities;Serial analyses of products of dissimilation of glucose show an increase in the rate of lactic acid formation and a decrease in the rates of formation of acetic acid, ethyl alcohol and carbon dioxide;The addition of acetaldehyde and acetylmethylcarbinol to fermentations of glucose results in an increased production of acetic acid and carbon dioxide and a decrease in the quantities of ethyl alcohol, lactic acid and glycerol formed. The added acceptors have no effect on fermentations by homo-lactic bacteria;The dissimulation of levulose by heterofermentative forms was similar to fermentations of glucose to which hydrogen acceptors had been added. Part of the levulose acted as a hydrogen acceptor; being reduced to mannitol;Two schemes of dissimilation are reviewed, one based on methylglyoxal as an intermediary and the other on phosphoglyceric acid. The data obtained in this study do not permit of the acceptance of one scheme to the exclusion of the other; either theory may be used to interpret the results. In view of the many mechanisms that may bring about the end-products in the same quantitative relationship and the isolation of intermediary compounds that do not satisfy a single scheme of dissimilation governs fermentation under all conditions. Further study should conciliate the various theories of carbohydrate breakdown and clarify the roles played by intermediary compounds such as methylglyoxal and phosphoglyceric acid.