174 FIXATION OR ASSIMILATION OF NITROGEN 



canum isolated by H. Pringsheim. It is a motile 

 organism of the " butyric " group which can carry on its 

 work under less stringent anaerobic conditions than 

 those necessary for C. pastorianum. In pure cultures in 

 open flasks it sets up carbohydrate fermentation with 

 nitrogen fixation, and in an atmosphere of hydrogen it is 

 able to ferment starch, mannite, and lactose. 



Benecke and Keutner described a large Clostridium 

 (C. gigantemn) from the soil, but its nitrogen fixing power 

 was not tested. The cells are pointed at the ends, and 

 some of them contain two spores. The spores of this 

 species are very large, being 2.5 /a long and 1.5 i* 

 broad. 



The power of nitrogen fixation appears to be a 

 common function of many organisms belonging to the 

 class which cause butyric-acid fermentations, but the 

 amount of combined nitrogen added to the soil by the 

 activity of these bacteria is probably small. 



For every gram of carbohydrate fermented from 1.2 

 to 3.7 milligrams of free nitrogen are assimilated. 



Ex. 89. Prepare the following solution : 



Di-potassium phosphate . . , . i gr. 



Magnesium sulphate . . . . . .5 gr. 



Sodium chloride \ 



Ferrous sulphate [ A very small crystal of each. 



Manganese sulphate J 



Dextrose . . . . . . 30 gr. 



Precipitated chalk . . .. . 30 gr. 



Water *. . . . . . . . i litre. 



Place 250 c.c. in four separate conical flasks, and inoculate 

 each with . 5 gr. of soil from four different localities. Close the 

 flasks with cotton wool plugs, and place them in the incubator 



