Recognizing early the importance of securing accurate body-temperatures in researches of this kind, a number of investigations were made and published elsewhere[15] regarding the body-temperature in connection with the experiments with the respiration calorimeter. It was soon found that the ordinary mercurial clinical thermometer was not best suited for the most accurate observations of body-temperature and a special type of thermometer employing the electrical-resistance method was used. In many of the experiments, however, it is impracticable with new subjects to complicate the experiment by asking them to insert the electrical rectal thermometer, and hence we have been obliged to resort to the usual clinical thermometer with temperatures taken in the mouth, although in a few instances they have been taken in the axilla and the rectum. For the best results the electrical rectal thermometer is used. This apparatus permits a continuous measurement of body temperature, deep in the rectum, unknown to the subject and for an indefinite period of time, it being necessary to remove the thermometer only for defecation.
As a result of these observations it was soon found that the body temperature was not constant from hour to hour, but fluctuated considerably and underwent more or less regular rhythm with the minimum between 3 and 5 o'clock in the morning and the maximum about 5 o'clock in the afternoon. In a number of experiments where the mercurial thermometer was used under the tongue and observations thus taken compared with records with the resistance thermometer, it was found that with careful manipulation and avoiding muscular activity, mouth breathing, and the drinking of hot or cold liquid, a fairly uniform agreement between the two could be obtained. Such comparisons made on laboratory assistants can not be duplicated with the ordinary subject.
It is assumed that fluctuations in temperature measured by the rectal thermometer likewise hold true for the average temperature of the whole body, but evidence on this point is unfortunately not as complete as is desirable. In an earlier report of investigations of this nature, a few experiments on comparison of measurements of resistance thermometer deep in the rectum and in a well-closed axilla showed a distinct tendency for the curves to continue parallel. A research is very much needed at present on a topographical distribution of body temperature, and particularly on the course of the fluctuations in different parts of the body. A series of electric-resistance thermometers placed at different points in the colon, at different points in a stomach tube, in the well-closed axilla, possibly attached to the surface of the body, and in women in the vagina, should give a very accurate picture of the distribution of the body-temperature and likewise indicate the proportionality of the fluctuations in different parts of the body. Until such a research is completed, however, it is necessary to assume that fluctuations in body-temperature as measured by the electric rectal thermometer are a true measure of the average body-temperature of the whole body. Indeed it is upon this assumption that it is necessary for us to make corrections for heat lost from or stored in the body. It is our custom, therefore, to compute the hydrothermal equivalent by multiplying the body-weight by the specific heat of the body, commonly assumed as 0.83, and then to make allowance for fluctuations in body-temperature.
When it is considered that with a subject having a weight of 70 kilos a difference in temperature of 1° C. will make a difference in the measurement of heat of some 60 calories, it is readily seen that the importance of knowing the exact body-temperature can not be overestimated; indeed, the whole problem of the comparison of the direct and indirect calorimetry hinges more or less upon this very point, and it is strongly to be hoped that ere long the much-needed observations on body-temperature can be made.
CONTROL EXPERIMENTS WITH THE CALORIMETER.
After providing a suitable apparatus for bringing away the heat generated inside the chamber and for preventing the loss of heat by maintaining the walls adiabatic, it is still necessary to demonstrate the ability of the calorimeter to measure known amounts of heat accurately. In order to do this we pass a current of electricity of known voltage through a resistance coil and thus develop heat inside the respiration chamber. While, undoubtedly, the use of a standard resistance and potentiometer is the most accurate method for measuring currents of this nature, thus far we have based our experiments upon the measurements made with extremely accurate Weston portable voltmeter and mil-ammeters. Thanks to the kindness of one of our former co-workers, Mr. S. C. Dinsmore, at present associated with the Weston Electrical Instrument Company, we have been able to obtain two especially exact instruments. The mil-ammeter is so adjusted as to give a maximum current of 1.5 amperes and the voltmeter reads from zero to 150 volts. The direct current furnished the building is caused to pass through a variable resistance for adjusting minor variations in voltage and then through the mil-ammeter into a manganin resistance-coil inside the chamber, having a resistance of 84.2 ohms. Two leads from the terminals of the manganin coil connect with the voltmeter outside the chamber, and hence the drop in potential can be measured very accurately and as frequently as is desired. The current furnished the building is remarkably steady, but for the more accurate experiments a small degree of hand regulation is necessary.
The advantage of the electrical method of controlling the apparatus is that the measurements can be made very accurately, rapidly, and in short periods. In making experiments of this nature it is our custom first to place the resistance-coil in the calorimeter and make the connections. The current is then passed through the coil, and simultaneously the water is started flowing through the heat-absorbing system and the whole calorimeter is adjusted in temperature equilibrium as soon as possible. When the temperature of the air and walls is constant and the thermal-junction system in equilibrium, the exact time is noted and the water-current deflected into the meter. At the end of one hour, the usual length of a period, the water-current is deflected from the meter, the meter is weighed, and the average temperature-difference of the water obtained by averaging the results of all the temperature differences noted during the hour. Usually during an experiment of this nature, records of the water-temperatures are made every 4 minutes; occasionally, when the fluctuations are somewhat greater than usual, records are made every 2 minutes.
The calculation of the heat developed in the apparatus is made by means of the formula C × E × t × 0.2385 = calories, in which C equals the current in amperes, E the electromotive force, and t the time in seconds. This gives the heat expressed in calories at 15° C. This procedure we have followed as a result of the recommendation of Dr. E. B. Rosa, of the National Bureau of Standards. In order to convert the values to 20°, the unit commonly employed in calorimetric work, it has been necessary to multiply by the ratio of the specific heat of water at 15° to that of water at 20°. Assuming the specific heat of water at 20° to be 1, the specific heat at 15° is 1.001.[16]
Of the many electrical check-tests made with this type of apparatus, but one need be given here, pending a special treatment of the method of control of the calorimeter in a forthcoming publication. An electrical check-experiment with the chair calorimeter was made on January 4, 1909, and continued 6 hours. The voltmeter and mil-ammeter were read every few minutes, the water collected in the water-meter, carefully weighed, and the temperature differences as measured on the two mercury thermometers were recorded every 4 minutes.
The heat developed during the experiment may be calculated from the data as follows: Average current = 1.293 amperes; average E. M. F. = 109.15 volts; time = 21,600 seconds; factor used to convert watt-seconds to calories = 0.2385. (1.293 × 109.15 × 21600 × 0.2385) × 1.001 = 727.8 calories produced.