1903.] 



On the Culture of the N Uroso-bacteriitm. 



361 



The salts are dissolved, and agar added to H per cent. ; the whole 

 being boiled up and prepared as ordinary agar. Magnesium carbonate 

 is added after sterilisation. 



As will be seen, this agar corresponds in composition to the ammonia 

 solution used for the ordinary cultures, save for the presence of the 

 1| per cent. agar. It has a slightly lower melting and coagulation 

 -point than bouillon agar. 



I have poured over 100 plates of this medium. It grows the nitroso- 

 "bacterium well, oxidation of the ammonia in the plate occurring within 

 2 months, as a rule, after inoculation with oxidised ammonia solutions. 



All plates that showed oxidation of the ammonia contained large 

 .numbers of colonies of apparently the same bacterium. This organism 

 being oval in form, and associated with the formation of nitrite, and 

 being often almost or altogether in pure culture, must be considered 

 to be the nitroso-bacterium. It occurred in the dilution plates in all 

 instances. Nevertheless but few of these showed oxidation of the 

 .ammonia. 



The following table gives results obtained : — 





Plates, number 



Number eb owing 





poured. 



oxidation. 





26 



22 





26 



3 



1 



26 



1 



This shows that unless the colonies were numerous nitrite was not 

 formed. 



In one instance a single colony taken from an ammonia agar plate 

 and placed on sloping ammonia agar formed nitrite in 9 months. Plates 

 •of beef-broth agar and gelatine poured from this culture grew enor- 

 mous numbers of the colonies. These colonies develop both at room 

 temperature and 37° C. At room temperature, after 6 days, the 

 ■colonies appear to the naked eye as white iridescent growths varying 

 in size. Some days later they become lemon coloured, and finally 

 yellow. Under the microscope they were seen to be made of micro- 

 organisms corresponding to the nitroso-bacteria. 



