86 AGRICULTURAL BACTERIOLOGY. 



some bodies are bringing them toward a condition for further 

 use, we can appreciate the extreme significance of these decom- 

 position bacteria in agricultural phenomena. 



Denitrification. But this general destruction of compounds 

 under the influence of bacteria produces evil as well as good 

 results. Not the high organic compounds alone suffer de- 

 struction, but some of the lower compounds of nitrogen are 

 similarly reduced, and among them, some which are of dis- 

 tinct value to plants. We have already seen that plants 

 obtain their nitrogen most easily in the form of nitrates and 

 next to this in the form of ammonia compounds. Now both 

 of these bodies, if present in the soil under the action of pu- 

 trefactive bacteria, undergo a further decomposition. We have 

 learned in recent years that some of the decomposition bacteria 

 are not only able to destroy the urea and proteids, but they 

 also have the power of extracting the oxygen from any nitrates 

 which may chance to be present, reducing them to a lower 

 form and rendering them useless for plant life. Some of the 

 soil organisms produce an even more complete destruction and 

 so act upon the ammonia compounds as to set the nitrogen 

 completely free from the compound. 



This general process is known as de nitrification. It always 

 results in the removal of oxygen from the nitrogen compounds 

 and in their consequent reduction to a lower state of organiza- 

 tion. For example the nitrates which are acted on become re- 

 duced to nitrites. If potassium nitrate (KNO 3 ) be present and 

 acted upon by the denitrifying bacteria it becomes potassium 

 nitrite (KNO 2 ). This denitrification has been most carefully 

 studied in the last five years since the importance of the phe- 

 nomenon has been realized. There were first discovered two 

 bacteria which produced this reduction in marked degree, and 

 they were named B. denitrificans I and //. Both of them 

 produce the reduction, but the No. II acts most energetic- 

 ally when in union with the very common bacterium B. 



