306 The Fixation of Nitrogen in Faeces 



From what source does this newly formed protein get its nitrogen ? 

 The most obvious answer is from the ammoniacal nitrogen derived 

 from the urine. But there is another possibihty. Atmospheric nitrogen 

 may have been fixed by the same process at work in the laboratory 

 experiments. Further there is some evidence that the substances 

 available as food for nitrogen fixing organisms can also nourish those 

 which convert ammonia into more complex forms. 



Both these actions may have gone on in the heaps of horse manure 

 during the first three months of storage, while the special food material 

 was available. In the second period of three months, after the exhaus- 

 tion of this special food, there is a considerable loss of organic nitrogen. 

 Cow manure on the other hand loses this form of nitrogen from the 

 first. 



The earlier experiments described above were all run for periods of 

 at least four months with the idea of giving the maximum opportunity 

 for nitrogen changes to occur, but it was not known how long fixation 

 took : whether action was complete in the first brief period or spread 

 uniformly over the whole interval. A series of flasks was therefore set 

 up each containing 5 grams of fresh horse faeces, 0- 1 gram calcium 

 carbonate, 0-1 gram of garden soil and 25 c.c. tap- water. Washed air 

 was drawn through them for about 3 hours daily as usual. At intervals 

 a flask was removed and the nitrogen determined. In most of the 

 previous experiments it was noticed that a distinct brown film formed 

 on the surface of the liquor after two or three weeks. Towards the end 

 of the present experiment the film was so tough that it required vigorous 

 shaking of the flask to break it. The nature of this scum will be referred 

 to later ; it is probably physical rather than biological in origin. The 

 question then arose, could the film cut off the supply of air to the bulk 

 of the fermenting substance and so limit the nitrogen fixation? The 

 inlet tubes of all the flasks used in these experiments delivered their 

 air close to, but not touching, the fermenting substance. The air did 

 not bubble through the solid or liquid. For the last eight weeks of this 

 experiment the inlet tubes of two of the flasks were pushed down 

 through the film so that the bubbling air should break it up. As the 

 figures in the following table show, the effect of this bubbling was to 

 increase to some extent the amount of nitrogen fixed. 



These figures indicate that the fixation of nitrogen was complete in 

 the first 28 days and that the maximum activity probably occurred in 

 the third week of the experiment. From the 28th to the 112th day the 

 amount of nitrogen fixed was verv uniform in all the flasks : the c;reatest 



