Mar. 1,1925 
Calorimetric Investigations with Cattle 
397 
the computed heat production where 
the body gains or losses are consider¬ 
able, and large differences where the 
gains or losses are comparatively 
small. It will be noted that in these 
tables the net gain in calories is given, 
and that the differences are somewhat 
obscured in those cases in which there 
was a gain of one substance and a loss 
of another by the algebraic addition of 
their energy equivalents. However, 
the separate consideration of the 
gains or losses of protein and fat 
does not materially alter the general 
relationship referred to above, since 
in most cases in which there was a 
considerable gain or loss of body 
tissue both fat and protein were gained 
or lost together. 
In those cases, at least, in which the 
gains or losses of body tissue are small 
and the differences between the ob¬ 
served and the computed heat produc¬ 
tion are large, if there is any serious 
error in the computed heat production 
it should be looked for in the analytical 
results. An examination of some of the 
analytical data recently obtained by 
the methods used in this institute has 
revealed possibilities of error which in 
the case of the experiments with cows 
deserve especial consideration. In these 
experiments there is, in addition to the 
problem of handling the milk, the 
necessity of collecting urine and feces 
together, thus giving rise to new diffi¬ 
culties in the handling and preparation 
of the samples for analysis. 
With this exception, essentially the 
same experimental procedure and ana¬ 
lytical methods were followed in the 
cow experiments as in the steer experi¬ 
ments (5, p. 200 -222) . It is important, 
however, to bear in mind the following 
points in connection with the compu¬ 
tation of the nitrogen, carbon, and 
energy balances: (1) In the steer ex¬ 
periments the nitrogen in the feces was 
determined in the fresh substance, while 
the carbon was determined in the air- 
dried sample, by means of a combustion 
furnace. (2) In the urine the carbon 
was determined in the fresh material, 
while the nitrogen was determined both 
in the fresh material and in a sample 
dried in the vacuum desiccator in the 
same manner as for energy determina¬ 
tion. From the nitrogen loss thus de¬ 
termined, in drying, an energy correc¬ 
tion was computed as applying to the 
energy determined by the bomb, assum¬ 
ing that the loss of nitrogen in drying 
represented a loss of urea and a corre¬ 
sponding loss of energy. 
In the cow experiments (except in 
221 a) 4 the feces were collected together 
with the urine. The nitrogen was 
determined in the composite of daily 
samples both in the fresh and in the 
air-dried materials in all cases, in order 
to ascertain the loss during drying. 
Carbon was determined in the air-dried 
sample by means of the bomb, in all 
cases, and also (in experiments 221g and 
221 f) in the fresh substance, by means 
of an electric combustion furnace. An 
attempt was made to determine the 
carbon in the fresh sample of the feces- 
and-urine mixture in the first of the 
experiments with cows, but owing to 
lack of laboratory help during the war 
and for some time thereafter, and to 
the initial technical difficulties with the 
method, no satisfactory determinations 
of the carbon in the fresh feces-and-urine 
mixture are available for the earlier cow 
experiments. The energy of the feces- 
and-urine mixture was determined in 
the air-dried sample. 
The air-drying was conducted by 
spreading the material out on trays in 
a drying closet in which it was exposed 
to a current of air heated to about 60° 
C. by passage over a steam coil. To 
hasten the drying the material was 
carefully broken up, when partly dried, 
by means of a spatula. When thor¬ 
oughly dry, the material (properly pro¬ 
tected) was exposed to the air of the 
grinding room for several days. It 
was then weighed, ground as rapidly 
as possible, and preserved for analysis 
in sealed, glass-stoppered bottles. In 
this weighing and grinding especially 
dry or especially damp days were 
avoided. 
LOSS OF NITROGEN AND CARBON IN AIR¬ 
DRYING FECES-AND-URINE MIXTURE 
A comparison of determinations of 
the daily nitrogen and carbon of the 
feces-and-urine mixture, in the fresh 
samples, with determinations on air- 
dried samples, revealed the fact that a 
considerable loss of these constituents 
occurred during the process of drying, 
and that the loss of carbon exceeded the 
quantity required to combine with the 
nitrogen lost to form either urea or 
ammonium carbonate. Table III ex¬ 
hibits these losses as occurring in experi¬ 
ments 221f and 221g. 
The figures in Table III show clearly 
that the carbon in the air-dried feces and 
urine is far from the original total, 
even after adding to it the carbon- 
equivalent of the nitrogen lost, com¬ 
puting this nitrogen to urea or ammo¬ 
nium carbonate. 
* In experiment 221a the feces and urine were collected together, in the calorimeter, while during the 
other days of the digestion period they were collected separately. 
