288 PRINCIPLES OF ANIMAL NUTRITION. 
The potential energy of food and excreta (that of the urine cor- 
rected to nitrogen equilibrium) and by difference the amounts of 
metahbolizable energy were: 
Urine Metaboliz- 
Food, F ; Methane, 
Eaads | TENE | ccorpestew,| Methane. | able Bneray. 
Period 7........ 46,275.0 | 14,104.8 2,593 .0 3,564.2 | 26,013.0 
OU, A sakes le 30,338 .1 8,574.9 1,795.0 2,579 .4 17,388 .8 
Difference ....} 15,936.9 5,529.9 798.0 984.8 8,624.2 
The metabolizable energy of the additional 3341 grams of or- 
ganic matter eaten in Period 7 was therefore 8624.2 Cals. This 
added food was intended to consist of hay, but the unavoidable 
variations in the moisture content of the feeding-stuffs resulted in a 
slightly greater consumption of the other ingredients of the ration 
also. Of the 3341 grams of additional organic matter, 3297 grams, 
as the previous table shows, were from the hay and 44 grams from 
the basal ration. If, then, we would ascertain the metabolizable 
energy of the added hay only, we must subtract from the difference 
of 8624.2 Cals. between the two rations the metabolizable energy of 
this 44 grams of organic matter from the other feeding-stufts. 
But while the gross energy of the latter is known, its metabo- 
lizable energy cannot be computed exactly, since it is impossible to 
determine what part of the energy of the excreta was derived from 
this particular portion of the ration. By assuming, however, that 
the same percentage of its gross energy was metabolizable as was 
the case with the basal ration, and that its non-metabolizable energy 
was similarly distributed between the various excreta, we may 
compute a correction which, although not strictly accurate, will not, 
in view of the small quantities involved, introduce any serious error. 
In this case the gross energy of the 3297 grams of organic matter in 
the added hay was 15,728.6 Cals., and the table takes the form 
shown on the opposite page. 
As thus computed, the metabolizable energy of the 3297 grams 
of organic matter added to the basal ration in the form of hay was 
8504.8 Cals., equal to 2.580 Cals. per gram. The total correction 
amounts to 119.4 Cals., and even a considerable relative error in it 
would not materially change the final results. 
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