USE OF AGAR SLANTS IN DETECTING AMMONIA 517 



of their own bodies. In the former case an ammonia determina- 

 tion may supply the missing infomiation. The organisms to be 

 thus tested may be growTi either on a synthetic medium contain- 

 ing no nitrogen except nitrate, or if they fail to grow under such 

 conditions on a nitrate-peptone medium. In the latter case a du- 

 plicate inoculation must be made on to a similar peptone medium 

 without nitrate to be sure that the ammonia is not produced from 

 the peptone. For a synthetic medium the writers recommend 

 that described by the Committee on the Descriptive Chart (1920) 

 except that glucose be substituted for sucrose as it is a more 

 available sugar than the latter and its presence is not confusing 

 when the Thomas test instead of the Nessler test is used to 

 detect ammonia. This medium is : 



Water 1.0 liter 



Agar 15 .0 grams 



Glucose 10.0 grams 



Potassium nitrate (other inorganic nitrogen sources may be 



used if desired 1.0 gram 



Calcium chloride 0.5 gram 



Dipotassium phosphate 0.5 gram 



If these tests are used in routine work for those organisms 

 that do not show nitrite as ordinarily tested in nitrate medium, 

 much valuable information can be obtained. It has been found 

 in this laboratory, for instance, that out of several hundred 

 cultures examined about 60 were nitrite-negative when grown on 

 nitrate-peptone agar. Of these 60 it was found, however, that 

 4 produced ammmonia on the above synthetic media without any 

 evidence of nitrite formation. By the usual methods such organ- 

 isms would be classed as non-reducers, whereas in the absence 

 of all other possible sources of ammonia, the positive ammonia- 

 reaction plainly indicates that they must have reduced the 

 nitrates to ammonia, and in such cases to class them as non- 

 reducers would be a decided error. 



As a routine procedure in connection with nitrate reduction 

 such a combination of tests shows promise of giving interesting 

 data on the physiological activities of bacteria. 



