It is generally accepted since PAsteur's studies of fermentation (1876) that a yeast, at least one capable of degrading sugars along a fermentative as well as a respiratory pathway, will make use of the energy provided by fermentative dissimilation when respiration is stopped by lack of oxygen. Nevertheless, molecular oxygen seemed to be indispensable for growth. PAsT~u~ himself already observed that growth of yeast under anaerobic conditions was rather restricted and was only possible when the inoculnm consisted of very young cells. The results of several later investigators on this subject confirm these observations. A few authors may be cited here. B~IJE~INCK (1893) considered yeast as a temporary anaerobe, that could perform only twenty to thirty generations under anaerobic conditions. F. Wr~DISCH (1932) stated that yeast may produce several generations under anaerobic conditions, but will need oxygen again at a certain moment. WHITE and MyNaS (1951) found that in the absence of oxygen only a few generations are possible, traces of oxygen being already very favourable for growth. CANTARELLI (1956) concluded that neither brewer's yeast nor baker's yeast can develop in the total absence of oxygen.
It seems thus that yeast, which means in these cases Saccharomyces cerevisiae or its close relatives, can grow, but not for an unlimited number of generations, under what is generally denoted as "anaerobic conditions", "absence of oxygen", etc., which expressions can only mean that the oxygen concentration is considered negligible. New viewpoints were given by A~D~ASEN and STIE~ (1953, 1954). These authors found that the presence of small amounts of ergosterol and oleic acid in the growth medium made possible the growth of yeast under an atmosphere of nitrogen containing less than I ppm oxygen.