TRANSFORMATIONS OF CARBON AND NITROGEN. 8/ 



coli communis. The No. II acts aerobically, the latter best in 

 the absence of oxygen. Since these two bacteria were studied 

 quite a number of others have been found, and about a dozen 

 have been described by bacteriologists as having especial 

 powers in this direction. Indeed it appears that most of the 

 bacteria which produce the putrefactive changes in decaying 

 proteids are capable, to a greater or less extent, of reducing 

 nitrates to nitrites if they are present in proper condition. 



Not only are nitrates thus reduced but the same bacteria, 

 or others, can act similarly upon the nitrites, taking out the 

 rest of the oxygen, and they can even act upon ammonia salts 

 in such a way as to free the nitrogen wholly from combination 

 and set it loose as free nitrogen. The latter process is not 

 quite so easily understood chemically, but experiment has 

 abundantly proved that it occurs, that the ammonia compounds 

 under the influence of denitrification are broken up and the ni- 

 trogen liberated. Apparently different species of bacteria are 

 concerned in the different processes. The bacteria shown in 

 Fig. 1 5 are common denitrifying bacteria. 



The extreme significance of this denitrification for the agri- 

 cultural industry is evident. Denitrification results inevitably 

 in nitrogen loss to the soil. If the soil be stocked abundantly 

 with nitrates and ammonia salts the denitrifying bacteria would 

 be able, if vigorously acting, to destroy them so thoroughly as 

 to leave the soil almost nitrogen-free. If denitrification goes 

 on in the manure heap it may largely destroy the nitrogen 

 compounds w r hich the farmer intends to use for fertilizers. The 

 importance of understanding the conditions under which this 

 process takes place most efficiently, and the conditions under 

 which it may be checked, is evident. In recent years bac- 

 teriologists have been earnestly investigating this phenomenon, 

 trying to learn how the nitrogen loss which arises as its result 

 may be prevented or diminished. This is not the place to 

 enter into the details of those investigations. One or two gen- 



