24 PRIMITIVE ANIMALS 



the production of nitrates from this organic ma- 

 terial is a complicated process brought about by 

 the concerted action of several kinds of bacteria. 

 When an organism dies, be it animal or plant, 

 its body cumbers the ground, and is at once the 

 seat of fermentative processes of decay, brought 

 about by the putrefactive bacteria, which break 

 up the complicated proteid materials of the body 

 into simpler nitrogenous substances and finally into 

 ammonia compounds. When the decay is complete 

 other bacteria attack the ammonia compounds and 

 form mineral nitrites from them, and by a further 

 process of oxidation a new set of bacteria convert 

 the nitrites into nitrates, and thus at last the nitrogen 

 has reached the form in which it can again be taken 

 up by the green plant and reassimilated into a living 

 body. Each step in this process is the work of a 

 special kind of bacteria, and were it not for the 

 activity of these organisms, the death of every living 

 body would mean a total loss of so much nitrogen to 

 life, so that in the end life would cease from nitrogen- 

 bankruptcy. 



Besides the power of getting at the nitrogen in 

 dead bodies and converting it finally into nitrates, 

 certain bacteria have the unique power of fixing 

 atmospheric nitrogen, thus actually increasing the 

 total available nitrogen for the use of life. These 

 bacteria play an important part in agriculture, as 



