32O STRUCTURE AND LIFE HISTORIES 
the nitrogen-fixing bacteria this process would continue 
until all complex nitrogenous compounds were reduced 
to ammonia or free nitrogen. All life would then cease, 
because green plants, upon which animal life is de- 
pendent, are unable to live without nitrogen, and they 
cannot utilize it in the form of ammonia nor of free 
nitrogen. Without chlorophyll and the nitrogen- fixing 
bacteria, therefore, all life would cease. Thus it is that 
life and death, health and disease, wealth and poverty, 
misery and happiness, are dependent upon the activity 
of tiny plants, too small to be seen, except under the 
highest powers of the microscope. 
