1. The main products of fermentation of 1,2-propanediol were n-propanol and propionic acid, but variable amounts of acetic acid and carbon dioxide were also formed. The concentrations of an intermediate propionaldehyde increased and then decreased.
2. A tentative scheme is suggested, showing that 1,2-propanediol is first dehydrated to propionaldehyde, which is then reduced to n-propanol. The scheme also explains the formation of propionic and acetic acids and shows how the metabolism of 1,2-propanediol is related to that of rhamnose.
3. Experiments with samples of rumen contents from animals on various diets showed that 1,2-propanediol was metabolized most rapidly when the animals were given molassed sugar-beet pulp. The rates of dissimilation of the diol increased with the concentration of rumen contents and with the concentration of substrate.
4. The dissimilation of 1,2-propanediol by rumen micro-organisms resulted in an increased uptake of hydrogen. The metabolic hydrogen, arising from the inhibition of methane production by chloroform, appeared to be better utilized than the gaseous hydrogen.
5. Oxygen gas did not affect the utilization of 1,2-propanediol, but the diol increased the uptake of oxygen by the rumen contents. The hydrogen and carbon balances were better when 1,2-propanediol was incubated anaerobically than in the presence of oxygen.