302 VEGETABLE PHYSIOLOGY 



exclusively with the word fermentation, was first observed 

 in connection with the life of the yeast-plant. It has how- 

 ever 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 supplements 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. 



Till quite recently it was held that alcoholic fermenta- 

 tion 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, which is secreted under conditions 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 has been 

 extended to include them, and the organisms themselves 

 have been called ferments. As however these processes have 

 come to be recognised as normal in many of the higher 

 plants, and to be carried out in them by the protoplasm of 

 particular cells, this peculiarity is seen not to be special to 

 the microbes and the fungi. The idea was soon transferred 

 to the protoplasm in general, and this property of setting 

 up anaerobic decomposition has become known as its 

 fermentative power. The very similar processes set up 

 through the enzymes which we have discussed in connection 

 with digestion, show us another manifestation of the same 

 fermentative power. All these processes can therefore be 



