FERMENTATION 307 
itself materially used up. Such a course would be much 
the more economical, not imvolving the consumption of 
much energy in reconstructive processes. This cannot, 
however, be regarded as finally established. 
The substance which seems most readily available for this 
purpose is sugar. Under the conditions mentioned it becomes 
decomposed or broken up entirely, the resulting products 
being carbon dioxide and alcohol. The process of alcohol- 
formation which was for so long a time associated exclusively 
with the word fermentation, was first observed in connection 
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 ig 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 hag 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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