The details of the bed calorimeter are better shown in fig. 4. The opening at the front is here removed and the wooden track upon which the frame, supporting the cot, slides is clearly shown. The tension equalizer (see page 71) partly distended is shown connected to the ingoing air-pipe, and on the top of the calorimeter connected to the tension equalizer is a Sondén manometer. On the floor at the right is seen the resistance coil used for electrical tests (see page 50). A number of connections inside the chamber at the left are made with electric wires or with rubber tubing. Of the five connections appearing through the opening, reading from left to right, we have, first, the rubber connection with the pneumograph, then the tubing for connection with the stethoscope, then the electric-resistance thermometer, the telephone, and finally a push button for bell call. The connections for the pneumograph and stethoscope are made with the instruments outside on the table at the left of the bed calorimeter. MEASUREMENTS OF BODY-TEMPERATURE. While it is possible to control arbitrarily the temperature of the calorimeter by increasing or decreasing the amount of heat brought away, and thus compensate exactly for the heat eliminated by the subject, the hydrothermal equivalent of the system itself being about 20 calories--on the other hand the body of the subject may undergo marked changes in temperature and thus influence the measurement of the heat production to a noticeable degree; for if heat is lost from the body by a fall of body-temperature or stored as indicated by a rise in temperature, obviously the heat produced during the given period will not equal that eliminated and measured by the water-current and by the latent heat of water vaporized. In order to make accurate measurements, therefore, of the heat-production as distinguished from the heat elimination, we should know with great accuracy the hydrothermal equivalent of the body and changes in body temperature. The most satisfactory method at present known of determining the hydrothermal equivalent of the body is to assume the specific heat of the body as 0.83.[14] This factor will of course vary considerably with the weight of body material and the proportion of fat, water, and muscular tissue present therein, but for general purposes nothing better can at present be employed. From the weight of the subject and this factor the hydrothermal equivalent of the body can be calculated. It remains to determine, then, with great exactness the body temperature.