PHYSIOLOGY OF THE MICROBES 



83 



experiment). There is even alcohol in animal tissues. There 

 is, therefore, nothing surprising in the presence of alcohol 

 throughout nature, in the soil, in water, in air, and in the sea ; 

 if it is true that the latter contains one millionth of its weight 

 (one gram per cubic metre) there must be an enormous 

 supply. 



Since the discovery by H. Buchner of zymase — the diastase 

 by which the yeast decomposes sugar — we know that it is on 

 the zymase rather than on the anaerobic conditions that the 

 alcoholic fermentation depends. But since the zymase only 

 appears when the yeast is shut off from the air, it too is 

 " an asphyxial function " and we return to Pasteur's formula. 



Duclaux has re-established the continuity between the two 

 methods of respiration by his idea of the constant operation 

 of the zymase in aerobic as much as in anaerobic life and by 

 maintaining that alcohol is produced by living tissues, not 

 pathologically but normally. " Alcohol is a normal and 

 necessary product in the digestion of the hydrocarbons of the 

 seed. When oxygen is present, this alcohol is burnt up and 

 escapes observation. To demonstrate it the plant must be 

 submitted to a degree 

 of asphyxia which just 

 lets it live, or rather, 

 which permits the action 

 of the zymase which it 

 contains. It is not the 

 asphyxia which pro- 

 duces the alcohol, it 

 only renders it per- 

 ceptible." 



Further, absolute 

 anaerobiosis does not 

 exist either in nature or 

 in our artificial cultures. 

 The pretty experiment 



of Denys Cochin shows that yeast even under anaerobic con- 

 ditions the most complete possible cannot do without oxygen 



G 2 



Fig. 36. — Cochin's experiment. 



