SPECIES OF AZOTOBACTER 175 



at 22 C. or 30 C. In a few days notice the active production 

 of gas bubbles. 



Suck up some of the chalk from the bottom of the flasks with 

 a pipette, spread out on a slide and examine with the microscope : 



1 i ) Are Clostridium forms present ? 



(2) Run under cover slip some iodine solution. Do the 

 bacteria stain with a blue colour ? 



(3) If spores are present stain as in Ex. 1 2. 



(4) Try and obtain growths of any of the organisms present 

 on potato under anaerobic conditions. (Buchner's tube 

 method.) 



2. Species of Azotobacter. In 1901 Beijerinck 

 isolated from soil and canal water two species of 

 organisms which are able to assimilate the free nitrogen 

 of the air and build up proteins and other nitrogen 

 compounds needed for the growth and development of 

 their bodies. These he included in a genus which he 

 named Azotobacter. By their multiplication they are 

 able to add considerable amounts of combined nitrogen 

 to the soil, which ultimately becomes available to farm 

 and garden cro|)s^thf6ugh the processes of decay and 

 nitrification, bin ce Beijerinck's discovery in 1901 much 

 attention has been devoted to the determination of the 

 distribution, growth, and conditions essential for nitrogen 

 fixation by these organisms. The different species are 

 readily isolated from almost every kind of soil except 

 those which are acid or of dry, sandy character. They 

 are also commonly present in well and river water and in 

 sea water, and are found on the surface slime of species 

 of Fucus, Laminaria, and other algae. Freudenreich and 

 Thiele found them in the soil down to a depth of 50 or 

 60 cm.; at 100 to 190 cm. deep Clostridium pas- 

 torianum was met with, but no species of A zotobacter. 



