36 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS. 
THE PURPOSE OF FERMENTATION. 
All these types of fermentations, whether caused by the metabo- 
lism of bacteria or yeasts, or by enzymes secreted by these organ- 
isms or by higher plants, are of vital importance in agricultural 
processes. Without their agency in breaking up organic com- 
pounds, the soil would rapidly become unfit for supporting life. 
The agricultural industry is not only dependent upon fermentations 
for many minor processes, but it is fundamentally dependent upon 
them for its continuance. While this is true, it must not be as- 
sumed that the various bacteria produce their results for the benefit 
of agriculture or for the benefit of the soil. There is no purpose 
in the matter. Each species of animal and plant acts its own life 
for its own good. If it secretes an enzyme that produces a fermenta- 
tion, this is done for its own benefit and not for the farmer's. The 
yeast ferments sugar, and bacteria putrefy proteids for uses of their 
own. Incidentally it may result that the natural processes of life 
phenomena are benefited thereby; but primarily all of the enzymes 
secreted and all of the fermentations produced are for the benefit of 
the organisms secreting them. If a bacterium or a mold secretes 
an enzyme into a lot of milk which causes its digestion, its purpose is 
to digest the milk for its own use and not for any incidental results 
that may accrue to the cheese-maker. 
