114 AGRICULTURAL BACTERIOLOGY. 



products of bacterial life which would otherwise escape by 

 volatilization. We may hold the ammonia by the use of acids 

 if this can be done cheaply and without injury to the manure 

 in other ways. We cannot hold the free nitrogen if it is loosed 

 from its combinations, and the only means of preventing this 

 loss is by checking the action of denitrifying bacteria. A satis- 

 factory method of accomplishing this has not yet been found, 

 but bacteriologists and chemists are now studiously at work 

 upon this problem of discovering some practical means of pro- 

 tecting the manure from its extensive losses. 



Constructive. As already noticed the process of denitrifica- 

 tion is eventually replaced by that of nitrification. This oc- 

 curs in the manure heap as well as in the soil. Exactly when 

 and why it begins is a little uncertain ; but it appears to start 

 only after the high organic compounds have been almost 

 wholly broken up into ammonia, and the ammonia formed has 

 either united with the acids to form salts or has been dissipated 

 into the air. Even while some ammonia is still present the 

 oxidation of the ammonia salts into nitrites is possible, for the 

 nitrous bacteria are not prevented from growing by the pres- 

 ence of free ammonia. The nitric bacteria are, however, so 

 extremely sensitive to ammonia that they cannot begin the for- 

 mation of nitric acid till ammonia gas has entirely disappeared 

 and therefore not until denitrification has wholly ceased. 

 When the nitrifying processes do begin they complete the 

 ripening of the manure. They oxidize the nitrogen compounds 

 which are left, the ammonia salts becoming first changed to 

 nitrites and then to nitrates. As this process continues the 

 manure heap is more and more filled with nitrates and there- 

 fore becomes a better and better food for plants. At last, 

 when the process is ended, the manure is fully ripened and its 

 nitrogen is so fully converted into nitrates that it furnishes a 

 most valuable supply of food for vegetation. If put upon the 

 soil it furnishes the soil both with plant food and with great 



