34 PRINCIPLES OF ANIMAL NUTRITION. 
Towards the interior of the body the differences became grad- 
ually less. 
It is evident, then, that the sources of possible error in ex- 
periments upon the influence of food on the composition of body 
fat are considerable, and that not only is great care necessary to 
secure representative samples of fat for examination, but the effect 
of individuality must be eliminated so far as possible by the use 
of a considerable number of animals. When we add to this the 
other fact that the fat production of herbivorous animals is 
largely at the expense of other nutrients than fat, we shall hardly 
incline to give the results of such investigations much weight as 
regards the question of the functions of food fat. 
QUANTITATIVE RELATIONS.—Some further light upon the point 
under discussion may perhaps be obtained from a consideration of 
the quantitative relations of food fat to fat production shown by 
respiration experiments and which will be considered more fully 
on subsequent pages (compare Chapter V). In scarcely any of these 
experiments has the food fat been deposited quantitatively: in 
the tissue. In three out of five experiments by Rubner in which 
fat was given to a previously fasting animal, from 65.82 to 91.89 
per cent. of the fat supplied in excess of the amount metabolized 
during fasting was stored up in the body. Similarly, in the ex- 
periments of Pettenkofer & Voit, in which the fat was added to a 
ration already more than sufficient for maintenance, on the average 
87.86 per cent. of the fat of the food was deposited in the tissues. 
Kellner,* among his extensive respiration experiments upon 
cattle, reports the results of three in which peanut oil was added to a 
basal ration more than sufficient for maintenance. The amounts 
of fat consumed in excess of the basal ration and the resulting gains 
by the animals were as follows, the slight variations in the amounts 
of the other nutrients being neglected: 
Gain by Animal. 
Additional Fat “ Gain of Fat 
Animal. Digested, in Per Cent. of Fat 
Grams. Protein, Fat, Digested. 
Grams. Grams. 
D 677 8 239 35.30 
F 542 86 205 37.83 
Qa 458 44 279 60.91 
* Landw. Vers. Stat., 58, 112, 124, 199, 214. 
