296 Plant Physiology 



products and wastes are far more abundant in anaerobic 

 respiration, owing to the lack of oxygen to stimulate the 

 changes resulting in the production of CO 2 and water. 

 With respect to micro-organisms which frequently demon- 

 strate anaerobic respiration, this subject is further dis- 

 cussed in succeeding sections upon fermentation. 



171. Fermentation. The original significance of this 

 term had reference to decomposition or change in or- 

 ganic substances, such as sugar solutions and cider, ac- 

 companied by the evolution of bubbles of gas, and 

 generally by the production of alcohol. After the work 

 of Pasteur and others, it was apparent that such changes 

 (although they may be due ultimately to enzyme action) 

 are in consequence of the activity of micro-organisms, 

 which are then defined as having the capacity to ferment 

 certain substances. 



In more recent times the term has applied to a variety 

 of types of decomposition due to microscopic organisms, 

 and also to the action of a large class of enzymes (soluble 

 ferments), whether obtained from micro-organisms or 

 from higher plants. The " ferment " action of the great 

 majority of enzymes does not involve the liberation of CO 2 . 



In general, fermentation phenomena may be regarded 

 as representing the various steps in decay. The type of 

 fermentation in any particular case is usually given the 

 name of the chief product produced, although in some cases 

 it is the group of substances acted upon which stands 

 sponsor for the name. In this chapter, only a few of those 

 fermentation phenomena are discussed that are induced 

 by the growth of micro-organisms, and as a result of which 

 alcohol and certain acids are produced. 



