THE USE OF AGAR SLANTS IN DETECTING AMMONIA 



PRODUCTION AND ITS RELATION TO THE 



REDUCTION OF NITRATES 



G. J. HUCKER AND W. A. WALL 



Neu) York Agricultural Experiment Station, Geneva, New York 



Received for publication June 9, 1922 



The use of agar slants in detecting the production of acid by 

 bacteria has been reported by our laboratory (Conn and Hucker, 

 1920) , and used successfully for some time. The determination of 

 such physiological activities on sohd media has many advantages 

 over the older methods in which hquid cultures were used and 

 especially is this true in the case of many of the free-living organ- 

 isms which either fail to grow or grow very poorly in liquid media. 

 As ammonia production by bacteria has an important significance 

 in assigning organisms to their natural groups, an effort has been 

 made to adapt some of the many ammonia tests to use with solid 

 media. One of the chief difficulties in employing the usual 

 methods has been the fact that the presence of certain organic 

 compounds interferes with the reaction and, as all cultural media 

 contain more or less organic material, satisfactory results could 

 not be obtained. This is especially true where Nessler's reagent is 

 used as this has a special affinity for organic nitrogenous material 

 especially the aldehydes. Because of this fact, it has been im- 

 possible to use glucose as a source of carbon in a medium in 

 which bacteria are grown to be tested for ammonia production. 



Bacteria in their metabolism are usually considered as securing 

 their energy from the oxidation of various carbon compounds, 

 while the nitrogen required to produce the bacterial protoplasm 

 is derived from various organic sources and in some cases from 

 inorganic compounds. The utilization of protein and other 

 organic sources of nitrogen, whether for energy or for protoplasm 

 building, is in many cases accompanied by free ammonia pro- 



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