THE FOOD AS A SOURCE OF ENERGY. 395 
A calculation similar to that made for the crude fiber yielded the 
following figures for the heat of combustion of the digested portion: 
Tein Sole eee ued 8.239 Cals. 
Desh” oa een ee eta ane 7.802 “ 
DEL coated wich gad wot apareh dane lack 8.185 “ 
LV soi sctlsetina ahaha Ahan Arka kane a eee 8.267 
Vv 8.685 “ 
That these results are more or less discordant is not surprising 
in view of the uncertain elements involved in the determinations. 
Applying the average figures for the energy per gram of the ether ex- 
tracts to the total amounts eaten and excreted in the five experiments 
taken together, we have for the average energy of the apparently 
digested ether extract 8.322 Cals. per gram, a figure considerably 
below the results recorded on p. 238 for either animal or vegetable 
fats. It must be remembered, however, that the ether extract of 
the feces contains more or less metabolic products, so that the 
above result does not represent the actual energy of the digested 
ether extract. It does, however, represent the energy correspond- 
ing to the difference between food and feces with which we reckon 
in computing rations, and from this point of view it is of value. 
NITROGEN-FREE Extract.—The nitrogen-free extract cannot 
be separated and examined like the crude fiber and the ether ex- 
tract, but it is possible to arrive at an estimate of its heat of com- 
bustion indirectly. For this purpose Kellner assumes the average 
heat of combustion of the proteids (proteid nitrogen 6.25) as 
5.711 Cals. per gram and that of the non-proteids as equal te that 
of asparagin, viz., 3.511 Cals. per gram. By subtracting from the 
gross energy of food or feces as directly determined the energy of 
the amounts of proteids, non-proteids, crude fiber, and ether ex- 
tract shown by analysis to be present, he computes the heat of 
combustion of the nitrogen-free extract. Furthermore, by compar- 
ing the results on food and feces as in the case of the crude fiber the 
heat of combustion of the digested portion may be computed. 
The results per gram of such a computation for the same four ex- 
periments were: * , 
* Loc. cit., 47, 303-306. 
Digitized by Microsoft® 
