Mar. 1, 1925 
Calorimetric Investigations with Cattle 
403 
grinding of the samples may be a source 
of appreciable error in the dry matter 
determination. However, the effect of 
an error in the dry matter of the feed, 
on the computed heat production, 
would be relatively slight, for the reason 
that the metabolizable energy and the 
energy of the body gain would be 
affected in the same direction. This is 
illustrated by the following computa¬ 
tion, the basis being arbitrarily assumed 
figures, and the effect on the nitrogen 
balance being disregarded: 
Daily ration.... 8,000 gm. air-dry matter. 
Error in dry matter.. +0.5 per cent. 
Energy per gram 
dry matter_4.5 Calories. 
Carbon in dry mat¬ 
ter_45 per cent. 
Error in the daily 
dry matter_+40 gm. 
Error in the metab¬ 
olizable energy_ 40X4.5=+180 Calories. 
Error in carbon bal¬ 
ance....+18 gm. 
Error in energy of 
the body gain_ 18X1.307X9.5=+223 Calories. 
Error in computed 
heat production... 180—223=—43 Calories. 
OTHER SOURCES OF ERROR 
The glycogen content of the 
body. —The computation of the energy 
equivalent of the gain by the animal 
assumes that the glycogen content of 
the animal remains unchanged. With 
a submaintenance ration, or in the case 
of milking cows, when the ration is not 
sufficient fully to support the milk 
production, the possibility of a con¬ 
tinuous loss of glycogen for some time 
may be considered. In the event of 
such loss the estimate for the energy 
equivalent of the body loss may be too 
large. In those cases in which there 
is a gain of body substance, after a 
considerable number of days of pre¬ 
liminary feeding on the ration of the 
experimental period to follow, the 
possibility that the glycogen content 
of the animal will come into equilibrium 
with the ration is greater, and the error 
involved in the assumption of a con¬ 
stant glycogen content of the body 
may not be appreciable. 
Carbon equivalent to the nitro¬ 
gen lost by the body. —Whether 
nitrogen be gained or lost by the body, 
it is considered to be accompanied by 
such an amount of carbon as is con¬ 
tained in an equivalent amount of 
protein, carbon being considered as 
constituting 52.54 per cent of the 
protein. The gain or loss in fat is 
computed from the carbon balance 
only after the carbon content of the 
protein gained or lost has been set 
aside. In case of a loss of protein, if 
there is a utilization of a part of the 
nonnitrogenous fraction of the katabol- 
izing tissue protein the amount so 
utilized is not accounted for, and con¬ 
stitutes an error in the computation of 
the carbon equivalent to the nitrogen 
lost and, likewise, in the carbon 
balance. 
Carbon dioxide of the water 
consumed. —The carbon dioxide con¬ 
tent of the water consumed b}^ the 
animal is usually not taken into con¬ 
sideration. This introduces a small 
error into the carbon balance, tending 
to reduce the apparent gain of carbon 
and to make the computed heat pro¬ 
duction too great. 
Heat of hydration and solu¬ 
tion. —Another small error is intro¬ 
duced in the determination of the 
energy of the visible excreta by neglect¬ 
ing the heat of hydration and solution. 
If heat is absorbed when solids come in 
contact with water, the reverse must be 
true, that is, heat is evolved when 
water is driven off. Conversely, if 
heat is evolved when solids are brought 
in contact with water, this heat must 
be absorbed on driving off the water. 
Thus, it is known that when urea is 
brought into solution an absorption of 
heat takes place, while when proteins 
are brought into contact with water an 
evolution of heat takes place. The 
feed is ordinarily given to the animal 
in an air-dry condition. Hydration 
and solution take place in the animal 
body, and corresponding evolution and 
absorption of heat must result. These 
processes may be considered as factors 
in the work of digestion. The energy 
of the urine, feces, and milk is deter¬ 
mined after these substances have been 
dried. The heat of hydration and 
solution is not accounted for in the 
determination. 
SUMMARY OF OBSERVATIONS ON SOURCES 
OF ERROR IN THE INDIRECT METHOD 
Errors on the following accounts are 
either unavoidable or are of negligible 
magnitude: Possible change in the 
glycogen content of the body of the 
animal; possible utilization of the non¬ 
nitrogenous portion of the katabolized 
protein molecule; and the energy of 
hydration and solution. 
It seems possible that errors due to 
the two factors first mentioned might 
be of appreciable importance in experi¬ 
ments in which the subjects are under 
submaintenance conditions. 
A small determinable error is intro¬ 
duced by the carbon dioxide of the 
drinking water. 
By far the most serious possibilities 
of error seem to lie in the methods of 
preparing the samples of feed, feces, 
