1 72 FIXATION OR ASSIMILATION OF NITROGEN 



suitable anaerobic conditions for its development and 

 growth. A mixture of the Clostridium and some aerobic 

 bacteria from the soil when grown in a medium contain- 

 ing 20 grams of dextrose and .01 gram of ammonium 

 sulphate, gave an increase of 24.4 mg. of combined 

 nitrogen, after the dextrose had all disappeared ; during 

 the experiment there was free access of air, from which 

 carbon dioxide and nitrogenous compounds had been 

 removed by passing through caustic soda and sulphuric 

 acid. 



Clostridium pastorianum belongs to the group of 

 bacteria which produce butyric acid, and resembles its 

 associates in morphology and in many of its physio- 

 logical powers. It can utilize as a source of energy for 

 its nitrogen-fixing process not only dextrose but levulose, 

 cane-sugar, galactose, and some other sugars. How it 

 obtains the necessary carbohydrate in the soil has not 

 been determined. Two sources appear to be possible, 

 namely, the residues from decaying plant tissues, or the 

 carbohydrate manufactured by minute green algae so 

 frequently met with in soil. The latter hypothesis is 

 the more likely, and is supported by evidence mentioned 

 later. According to Winogradsky, it does not form 

 butyl alcohol nor ferment mannite, starch, lactose, or 

 calcium lactate, in these respects differing from the 

 common representatives of the " butyric " group. In an 

 active state of growth the organism is a short cylindrical 

 bacillus 1.5 to 2 //, long and 1.2 to 1.3 ^ broad, with 

 little or no motile power, and stains yellow with iodine 

 solution. After further development it becomes an oval 

 or spindle-shaped organism of the usual " Clostridium " 

 form, with granular contents ; in this stage it contains 

 granulose, a carbohydrate which closely resembles starch, 



