Pyroracemic acid is converted into succinic acid when perfused through mammalian muscle; moreover, more formic acid is always found than in control experiments. Acetic acid and acetaldehyde can be excluded as intermediate products. As the reaction only takes place in the presence of O it is suggested that the pyroracemic acid is dehydrated and then polymerises; the polymerisation product is hydrolyzed into succinic and formic acid. It is suggested that the metabolism of sugar occurs as follows: (1) Hexosemonophosphoric acid, (2) Reactive form of glucose, (3) 2 molecules methyl glyoxal, (4) 2 molecules pyroracemic acid, (5) Polymerisation product (with dehydration), (6) Succinic acid +2 molecules formic acid, (7) Fumaric acid, (8) Malic acid, (9) Oxalacetic acid, and (10) Pyroracemic acid. The hydrolysis of [alpha]-ketonic acid is of significance in protein and fat metabolism, as [alpha]-amino acids are converted into a-ketonic acids after deamination and as it has been shown by perfusion experiments that formic acid arises from acetic acid, the chief decomposition product of fatty acids. It is also suggested that acetic acid is converted into glyoxalic acid and this, after removal of water, is converted into 2 molecules of formic acid.