270 



Microbes and You 



THE NITROGEN CYCLE 



Nitrogen, as an element of protein, is a constituent of every 

 living cell. Unless there were some means for releasing nitrogen 

 and other elements from dead plant and animal cells, the world's 

 supply of available elements would in time be bound up and un- 



NITRATES 



AMMONIA 



ANIMAL 

 PROTEIN 



PLANT 

 PROTEIN 



Fig. 47. The nitrogen cycle. 



available for future generations of living things. Through the 

 action of microbes, bacteria in particular, the elements are kept 

 rotating in a so-called cycle. 



Commencing at the bottom of the diagram depicting the nitro- 

 gen cycle, labeled animal protein, it can be seen that at least two 

 paths are available as the cycle is followed clockwise. During the 

 metabolism of higher animals one of the waste products, excreted 

 principally through the urine, is urea, which has the chemical 

 formula CO(NH2)2- When urea is acted upon by microorganisms 



