302 The Fixation of Nitrogen in Faeces 



Having established the fact that nitrogen fixation actually occurred 

 during aerobic fermentation of the horse faeces, the next step was to 

 compare the behaviour of bullock and cow faeces under similar con- 

 ditions. It is well known that the horse does not digest its food as 

 thoroughly as the bullock. On the assumption that the nitrogen fixing 

 organism derives its nutriment from the imperfectly digested carbo- 

 hydrate in the fresh faeces, the amount of nitrogen fixed in bullock 

 and horse dung should be in inverse relation to the digestive efficiency 

 of the animals. The tap-water used in these experiments contained 

 much calcium carbonate which apparently favoured nitrogen fixation, 

 for it proved more effective than distilled water. To test this point 

 one of each pair in the next series of experiments was made up with 

 distilled instead of tap-water. The results of 134 days' fermentation at 

 laboratory temperature are set out below. 



Comfarative fixaiion of Nitrogen in Horse and Bullock faeces. 



Weight of substance taken (grams) 

 Original total nitrogen (grams) 

 Final total nitrogen ... 



Difiference ... 



Per cent, of original total N 



The figures suggest that the view just put forward is sound, as the 

 bullock droppings fixed less than a quarter the amount of nitrogen 

 gained by the corresponding samples of horse faeces. Distilled water, 

 again, had a marked depressing action compared with tap-water. 



It is obvious that the diet of the animals must influence such results 

 considerably. In this case the horses were receiving the ration of hay 

 and oats usual for work on the farm, and the bullocks were on grass 

 with about 5 lbs. of mixed cotton and linseed cake per head per day in 

 addition. 



The effect of a purely grass diet on the nitrogen fixing power of 

 horse faeces was tested in two experiments with the following results : 



Horse faeces on grass. 



Weight of substance taken (grams) 

 Original total nitrogen (grams) 

 Final total nitrogen 



Difference 

 Per cent, of original total N. ... 



