iqiq] 



BOX. 1 ZZI—XI TRIFICA TION 



205 



the vitality of the cultures were made by inoculating all the 

 heated material in large test-tubes containing 25 gm. of sterile 

 coarse ignited soil and MgC03 kept in a slanting position by 10 cc. 

 of sterile O^elianski solution. Duplicates were run for each 

 treatment. \\Tien the cultures were tested for the formation of 

 nitrite after 12 days of incubation at 30° C, the results given in 

 table III were obtained. 



Although the duration of incubation was not very long, the 

 nature of the medium was such as to allow complete nitrification 

 in all cases where full inoculum was used. The fact that a 

 heating of 40 minutes at 50° C, a heating of 10 minutes at 55° C, 



TABLE III* 



Temperature of heating 



Time of heating in minutes 



45° C 



50° C 



55° C... 

 62-65" c. 



+ 

 + 

 + 



+ 



+ 



+ 



o 



+ 



+ 



? 



+ 

 + 



40 



+ 

 o 



60 



+ 



*The + indicates a strong nitrite formation, ? a questionable nitrite formation, and o no 

 nitrite formation. 



and a heating of 5 minutes at 62-65° ^- g^^'^ questionable or 

 negative nitrification, while all other cultures gave complete nitri- 

 fication, is very significant. 



BouLLAXGER and Massol (3) found the thermal death point 

 of the organism of nitrosofermentation isolated in their work to 

 lie between 45° and 50° C. when the heating continued for 5 min- 

 utes. It is seen, therefore, that the organism isolated from Woos- 

 ter soils resists higher temperatures and longer periods of heating 

 than the one which constituted the object of their studies. The 

 difference in apparatus used might lead to slight variations in 

 the T.D.P. determinations. 



The incubation of all the cultures of nitrite-formers cultivated 

 in this laboratory has been done at 28-30° C. At this tempera- 

 ture cultures were obtained which nitrified as much as 8 . 04 mg. 

 of ammoniacal nitrogen in 26 days of incubation at rest. 



