334 PRINCIPLES OF ANIMAL NUTRITION. 
molasses (p. 291), the difference in the metabolizable energy of the 
excreta is the algebraic sum of the differences in the energy of 
methane, urine, and the several proximate ingredients of the feces, 
and some of these differences may be positive and others negative. 
The computations of the metabolizable energy of the organic matter 
as made in the earlier paragraphs give the net result to the animal 
under the condition of the experiment and include all the secondary 
effects upon digestion, ete. 
In the computations here considered Kellner’s methods have 
been followed. In the first place the influence of the added feed 
upon the digestibility of the basal ration has been eliminated by 
basing the computation upon the digested matter. Still further, 
such effects as the decrease of the methane excretion in certain of 
the experiments with molasses, oil, and starch, and the diminished 
export of energy in the urine under the influence of starch and ex- 
tracted straw, have not entered into the computation. In other 
words, the endeavor has been to determine the actual amount of 
energy liberated by the breaking down of the molecules of the di- 
gested starch or protein or fat in the organism without regard to 
these various incidental effects; that is, to determine the real and 
not the apparent metabolizable energy. 
Either method of computation would seem to be entirely defensi- 
ble, and our choice between them will be largely determined by 
the point of view. For the purposes of the physiologist, desirous 
of tracing the details of the chemistry and physics of metabolism, 
the results obtained by the latter method will be of more interest. 
On the other hand, the student of nutrition who is especially in- 
terested in the problems of feeding will not fail to note that the 
results thus reached represent, from his standpoint, only a part of 
the truth. They show (barring errors of detail) how much energy 
is liberated in the body from the several nutrients, but the loss or 
saving of energy in the incidental processes constitutes just as real 
a part of the balance of energy which he wishes to determine as the 
energy liberated from the nutrients themselves, and must be taken- 
account of in his calculations. Whether this can best be done by 
using some such factors as those just tabulated and then making 
a correction for these incidental gains and losses, or whether the 
method followed in the earlier paragraphs is to be preferred, it 
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