307 



"If <Q*. " < <^s 



itself materially used 

 the more economical, 

 much energy in recons 

 however, be regarded as fii 



The substance which seem] 

 purpose is sugar. Under the coi 

 decomposed or broken up entire! 

 being carbon dioxide and alcohol, 

 formation which was for so long a time assocl 

 with the word fermentation, was first observed in connect 

 with the life of the yeast-plant. It has, however, since 

 been ascertained to be much more widespread, and to be 

 indeed the most common of the anaerobic respiratory 

 processes. In cases where the metabolic activities are very 

 great, as in germinating peas, we find this process supple- 

 ments the ordinary respiration, for alcohol can be detected 

 in their cells in small quantities. The same thing has been 

 noticed in the leaves of the vine. We must suppose here 

 that the amount of oxygen absorbed is insufficient for their 

 requirements, and that partial asphyxiation results. The 

 swelling of the germinating seed partly occludes its inter- 

 cellular spaces and so hinders the access of oxygen to the 

 cells of the interior. 



It was for a long time held that alcoholic fermentation 

 was conducted exclusively by the activity of the proto- 

 plasm of the cells in which it was observed. It has been 

 ascertained, however, that it may also be caused by the 

 action of an enzyme zymase, which is secreted under con- 

 ditions of incipient asphyxiation by many cells, and which 

 is formed in the yeast-plant even in the absence of such 

 stimulus. 



Though the term * fermentation ' was originally applied 

 and confined to the formation of alcohol, it is now usual to 

 extend it far more widely. Many other processes of similar 

 nature have been discovered, nearly all of which at first 

 were found to be carried out through the agency of microbes 

 or higher fungi. Hence the meaning of the term was 



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