578 JOHN R. MURLIN 



away by the water current. To this must be added the latent heat in the 

 water of vaporization and any heat stored in the body itself. 



For the measurement of this latter quantity an electrical resistance 

 thermometer is inserted into the rectum to a depth of 10 or 12 cm. Fluc- 

 tuations in the body temperature can thereby be followed accurately by 

 readings on the Wheatstone bridge. If the body temperature rises during 

 the course of a period of observation the amount of'heat stored is found by 

 multiplying the rise in temperature by the weight of the body and by 

 the specific heat of the animal body (0.83). Should the body temperature 

 fall, heat will be given up to the calorimeter and may be deducted by a 

 similar calculation. 



The temperature of the ingoing air must likewise be adjusted so as 

 to be at all times equal to the temperature of the outgoing air ; otherwise, 

 heat would be added to or taken away from the chamber by the air cur- 

 rent. Thermal junctions are so placed as to have one terminal in the 

 outgoing air and the other in the ingoing air immediately adjacent to 

 the calorimeter so that any difference in temperature of the two air cur- 

 rents is instantly detected by connecting the circuit with the galvanometer. 

 A cooling effect in the ingoing air is brought about by means of a continu- 

 ous current of water running at a very slow rate against which a warming 

 effect produced by an electric lamp is kept in action. 



Finally heat may be stored in the calorimeter itself. To detect such 

 a change resistance thermometers are attached to the inner walls of the 

 calorimeter and if the temperature of these walls rises or falls between 

 the beginning and the end of an experiment a correction is made. With 

 the chair calorimeter it has been found that 19.5 Calories of heat are ab- 

 sorbed when the inner wall rises one degree of temperature. Conversely, 

 19.5 Calories are lost by the wall when the temperature falls one degree. 

 This quantity is known as the hydrothermal equivalent of the calorimeter. 

 For the bed calorimeter of Benedict the hydrothermal equivalent is 21 

 Calories; for the Sage calorimeter at Bellevue 19 Calories. When all of 

 these corrections are made the result gives the amount of heat actually 

 produced by the body in the period of observation. 



a. Control Tests. A calorimeter must be very carefully controlled as 

 regards its heat measuring capacity. What is known as a "heat check'' 

 is run in the following manner : A current of electricity of known voltage 

 is run through a resistance coil placed inside the respiration chamber. To 

 secure uniformity in the electrical current and therefore in the amount of 

 heat dissipated, Williams used an accumulator battery as a source of 

 current. This battery was of sufficiently large capacity (about 45 ampere- 

 hours) to deliver the required amount of energy over periods of four or 

 five hours without much diminution in voltage. The current passes from 

 the battery through a ballast resistance, then through the heat coil and 

 back through a standard resistance. A precision milli-voltmeter measures 



