158 RESPIRATION 



oxygen respiration. On the other hand, distillers' top fer- 

 mentation yeast was found to ferment only 80 per cent, of 

 the sugar available, the remaining 20 per cent, being oxidized. 

 In wild yeasts, Torula so called, oxygen respiration is much 

 higher, and in these plants oxygen is able to depress alcoholic 

 fermentation to extinction. These observations provide ex- 

 perimental proof of Pasteur's thesis " la vie sans air " which 

 he could not establish owing to his use of a yeast whose oxygen 

 respiration was too small for detection by his experimental 

 procedure. 



Meyerhof also showed that for each molecule of oxygen 

 taken up in the oxygen respiration of yeast, one molecule 

 of sugar less is fermented, but, since according to the 

 equation 



C 6 H 12 O fl + 60 2 = 6C0 2 + 6H 2 



one molecule of oxygen is only able to oxidize one-sixth of a 

 molecule of sugar, it would appear that the oxidation of only 

 one-sixth of a molecule of sugar is sufficient to protect from 

 fermentation one molecule of sugar; otherwise expressed, 

 one molecule of sugar by oxidation protects six molecules 

 from fermentation, a figure approximately equivalent to that 

 found by Meyerhof and by Hill to hold good for muscle 

 contraction. 



The close connection between the chemical changes in 

 muscle and those occurring in alcoholic fermentation is shown 

 by the fact that yeast whose fermenting power has been 

 destroyed by washing out the thermostable coenzyme can 

 be restored to activity by the addition of an aqueous extract 

 of muscle ; similarly, the addition of the coenzyme of yeast 

 to a washed muscle will restore its power of respiration. 



Furthermore, in both there is an intermediate formation 

 of a hexose phosphate, which in muscle gives rise to lactic 

 acid, and is hence termed lactacidogen, but in fermentation 

 gives rise to alcohol. 



If respiratory processes are essentially enzymatic, it is 

 natural to suppose that the respiration intensity would increase 

 in the presence of accelerators : various substances have been 



