For many years bacteriologists have observed
that some bacteria produce acid from carbohydrates
only under aerobic conditions while others
produce acid both under aerobic and anaerobic
conditions. The significance of these observations
does not seem to have been appreciated generally
by taxonomists. Studies of bacterial physiology
have made it increasingly evident that the bacterial
metabolism of carbohydrates may be accomplished
by two apparently fundamentally
different mechanisms (see for example Porter,
1946; Werkman and Wilson, 1951).