. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . identical process being one of oxidation, the access of air is necessary. Denitrification.—^This is a reducing process. The nitrate is madeto yield up a part or all of its oxygen and thus becomes changed, tonitrites and to ammonia and even to free nitrogen. The partial changedoes not rob the soil of its available nitrogen as does the total change,for the nitrites and ammonia may be changed by the nitrifying bacteriato nitrates. These bacteria exist normally in most soils and are espe
. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . identical process being one of oxidation, the access of air is necessary. Denitrification.—^This is a reducing process. The nitrate is madeto yield up a part or all of its oxygen and thus becomes changed, tonitrites and to ammonia and even to free nitrogen. The partial changedoes not rob the soil of its available nitrogen as does the total change,for the nitrites and ammonia may be changed by the nitrifying bacteriato nitrates. These bacteria exist normally in most soils and are especiallyabundant in manure. There are three different types of nitrogenreduction: (1) The reduction of nitrates to nitrites and ammonia. (2) The reduction of nitrates and nitrites to gaseous oxides of nitrogen. (3) The reduction of nitrites with the development of free nitrogen Bacteria.—Helbrigel, in 1886, demonstrated that cer-tain plants were able to use the nitrogen of the air and this apparentlythrough the aid of bacteria growing in their roots. These root bacteria. NITRIFICATION 651 are named B. radidcola. They produce enlargement (tubercles) onthe roots. According to Ball, there is no reasonable doubt but that B. radidcolacan and usually does remain active for very long periods in soil devoidof leguminous vegetation. Furthermore, the bacterium diffuses at avery considerable rate through soils that are in proper condition;therefore if a soil should be found lacking the organism, it is illogicalto attempt to introduce it artificially without having first made thesoil fit for the development of the bacteria. It has not been shown by anyone that increased powers of resistanceto unfavorable conditions of certain varieties are at all correlatedwith their enhanced greed for nitrogen. Moreover, it is far frombeing proven that any one race or physiological species is really morevirile than another. Greig-Smith has shown that as many as threeraces are someti
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