310 The Fixation of Nitrogen in Faeces 



any experiment of the two series. It seems probable that the nitrogen 

 fixation is only the last link in a chain of biological changes brought 

 about by organisms normally present in the faeces or soil. 



Since Azotohader alone is unable to fix any appreciable amount of 

 nitrogen in faeces, while in combination with B. lactis aerogenes it will 

 fix three times as much nitrogen as a pure culture of Azotohader, both 

 grown in dextrose, and further, inoculation of raw faeces with the 

 mixed organisms does fix a considerable amount of nitrogen, it may be 

 concluded that these two organisms play some part in the changes 

 observed in these experiments. 



Has the nitrogen fixation noticed in these experiments any practical 

 significance? The direct effect is probably small. At most it means 

 that when a soil is manured with horse dung there is a possible addition 

 of atmospheric nitrogen which may amount under the most favourable 

 conditions to 30 % of the nitrogen in the complete manure. The 

 quantity of stable manure applied to arable soil is small and is steadily 

 diminishing as the motor replaces the horse for road traction. The 

 amount of nitrogen that could possibly be fixed in this way is practically 

 negligible. Any value seems rather to lie in the evidence that appreci- 

 able nitrogen fixation can occur under conditions generally held to be 

 unfavourable for this form of bacterial activity. There are industrial 

 by-products containing actual or potential food for organisms of the 

 types working in horse faeces. Obviously many difficulties must be 

 overcome before any use can be made of waste material in the way 

 indicated, but it is along these lines that any attempts to increase the 

 quantity of atmospheric nitrogen normally added to the soil should 

 have some chance of success. 



Conclusions. 



1. Horse faeces contain material capable of fixing nitrogen when 

 fermented aerobically in presence of sufficient moisture and calcium 

 carbonate. 



2. This fixation is a function of the diet, for when horses are fed 

 on grass alone, instead of corn and hay, the amount of nitrogen fixed 

 is much reduced. 



3. Under the most favourable conditions 1 gram of dry matter in 

 the faeces will fix 4 mgms. of nitrogen. 



4. Bullock faeces will also fix nitrogen but to a much smaller 

 extent than horse faeces. This is also a function of the diet as it only 



