_Calorimeter_
At the conclusion of these experiments, the accuracy of our
calorimetry apparatus was tested by burning an ethanol lamp in the
metabolism chamber. During these tests a CO_{2} analyzer was
incorporated into the system (Beckman, LB-2). Results demonstrated
that we measured 84% of the oxygen consumed by the lamp as well as 84%
of the water and CO_{2} it produced; standard deviation = +-2.6, +-5.0,
and +-3.6, respectively (n = 27). Average respiratory quotient (RQ)
calculated from these data was O.657 +-0.008 (n = 27), which is 99.5%
of that predicted (0.66). McNab (1988b) reports that the accuracy of
open-flow indirect calorimetry systems, such as ours, depends on the
rate of air flow through the animal chamber. If flow rates are too
low, there is inadequate mixing of air within the chamber, and the
rate of oxygen consumption, as calculated from the difference in
oxygen content of air flowing into and out of the chamber (Depocas and
Hart, 1957), is underestimated. At some critical rate of air flow,
which is unique to each combination of chamber and animal, this
situation changes such that measured rates of oxygen consumption
become independent of any further increase in flow rate (McNab,
1988b). In recent tests of our system, where we burned the ethanol
lamp at a variety of chamber flow rates, the efficiency of
measurement increased linearly as flow rate increased, and the
critical rate of air flow was about 6.7 L/min. This appeared to
explain why a flow rate of 3.0 L/min underestimated oxygen consumption
of the ethanol lamp.
Our earlier tests of the efficiency of our system indicated that
although we underestimated actual oxygen consumption of the ethanol
lamp, we did so with a fair degree of precision; probably because flow
rates were closely controlled. During our metabolic measurements,
chamber flow rates also were closely controlled at 3.0 L/min, and we
believe, therefore, that these measurements also were carried out with
a high degree of precision. Consequently, all measured values of
oxygen consumption and water production were considered to be 84% of
their actual value and were adjusted to 100% before being included in
this report.
_Body Temperature Transmitters_
The calibration of all temperature-sensitive radio transmitters
drifted over time. Transmitters were calibrated before they were
surgically implanted and again after they were removed from the
animals. Although the drift of each transmitter was unique, it was
also linear (S. Tomkiewicz, Telonics, Inc., pers. com.). All body
temperature measurements were corrected from timed extrapolations of
the difference between starting and ending calibrations.