RECLAIMING LOST NITRO(,KN. l6l 



most cases, to assume the form of carbon dioxide, which at 

 once becomes dissipated into the atmosphere, keeping up the 

 store of this gas which forms the basis of plant life. In this 

 destruction of organic bodies they also reduce the nitrogen to 

 a variety of simple nitrogenous compounds. Ammonia is pro- 

 duced in large quantity, and not a little of the nitrogen, in 

 the form of free nitrogen, is completely separated from its com- 

 binations to join the atmospheric supply. Other nitrogenous 

 bodies of low state of chemical combination are doubtless also 

 formed. 



4. Bacteria of a different nature seize these end products of 

 decomposition and build them up into nitrates. This process 

 occurs, according to our present knowledge, in two stages and 

 under the influence of two different bacteria species. By one 

 process the ammonia is oxidized to nitrites, and by the second, 

 the nitrites are oxidized to nitrates. This process of nitrifica- 

 tion lies at the basis of soil fertility, inasmuch as it is the 

 means by which the low nitrogen compounds, resulting from 

 decomposition of organic matter, are worked over and built up 

 into the form of nitrates when they may again act their role 

 in organic life. This process of nitrification goes on only in the 

 absence of large quantities of organic food. It occurs in the 

 soil if the amount of organic food is not too great, but will not 

 occur while the active decomposition, due to putrefying bac- 

 teria, is taking place. 



5 . Bacteria, acting in connection with the legumes, reclaim from 

 the atmosphere much of the lost nitrogen. In spite of every 

 method at our disposal there is always a loss of nitrogen from 

 the state of combination ; but this nitrogen may be fully re- 

 placed in the soil for the use of plants by the agency of bac- 

 teria. In addition to the bacteria that are capable of assimi- 

 lating the free nitrogen directly and fixing it in the soil, there 

 is a second type of bacteria which acts in connection with the 

 legumes, forming a relation which we call symbiosis. The 



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