NITRIFICATION 151 



look like very small watery drops with granular contents : the 

 deep ones are exceedingly small, brown, kidney or spindle 

 shaped. The larger colonies observed are generally impurities. 

 Transfer some of the smallest colonies by means of capillary 

 tube (Ex. 78 c. ii) to flasks of the nitrite solution, using low- 

 power microscope for selection of the colonies, and 



1 i ) test for disappearance of nitrite and appearance of nitrate ; 



(2) examine a drop of the solution and note the form and size 



of organisms observed ; 



(3) -inoculate ordinary slightly alkaline bouillon and note if 



turbidity and growth occurs ; carry on the incubation at 



30 C. for two weeks at least. 



From cultures which are bouillon sterile the organisms may 

 be obtained and stained with carbol fuchsin : they are usually 

 rod-shaped, about i /-/- long and .3 to .4 //, thick, or in 

 some instances somewhat oval and i to 1.5 p long and up to 

 .8 /x thick. 



