156 A RESPIRATION CALORIMETER. 



Measurements of body temperature. In experiments in which the heat 

 production is determined, it has been commonly supposed that the body 

 temperature at any given hour of the day is practically the same from 

 day to day. Inasmuch as the body temperature undergoes a daily 

 fluctuation, with a minimum in the morning, usually between 2 and 4 

 o'clock, and a maximum in the afternoon about 5, a true measure of 

 the heat production by short periods (two or three hours) can only be 

 determined by making corrections for changes in body temperature at the 

 beginning and end of any given period. To ascertain these fluctua- 

 tions of temperature, a special form of thermometer, based on variations 

 in electrical resistance, was devised. The thermometer, its calibration 

 and method of use, and a large number of observations made with it 

 are described in detail elsewhere. 1 An illustration of the apparatus and 

 a brief description of it are here given. 





FIG. 45. Rectal Thermometer. A coil of fine platinum or copper wire inclosed in a pure silver 

 tube is connected by an incandescent lamp cord to two metal plugs which fit in a switch. About 

 20 cm. of the other end is covered with rubber. 



A coil of fine double-silk covered wire (either copper or platinum), 

 having a resistance of about 20 ohms, is inclosed in a small silver 

 tube 30 mm. long and 5 mm. in diameter. The two ends of a flex- 

 ible cable pass through a hard-rubber plug in the end of the silver 

 tube and connect with the coil. A piece of soft- rubber tubing is slipped 

 over the flexible cable and the ends well fastened with silk and shellac. 

 The thermometer may then be inserted some 10 to 12 cm. in the rectum 

 and worn with little inconvenience to the subject. The cable is connected 

 with the plug switch and the variations in resistance of the rectal ther- 

 mometer are measured by one of the bridge systems in the special form 

 of mercury switch previously described. (Seep. 148.) Fluctuations of 

 one-hundredth of a degree Centigrade can be readily determined, 

 is thus possible to have observations of the body temperature of the 

 subject within the respiration chamber recorded independently by the 

 observer outside of the chamber. Observations are usually made every 

 4 minutes. 



1 Archiv. f. d. g. Physiol. (Pfluger), 1901, 88, pp. 492-500, and 1902, 90, pp. 33-72. 



