THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 155 



so complete as could be desired. A tentative figure, which is, however, 

 little more than a rough estimate, is 30 calories. In practice it has 

 been our custom to add 30 calories to the heat measured during the 

 period from 1 1 p. m. to i a. m. , and to deduct 30 calories from the heat 

 measured during the period from 7 a. m. to 9 a. m. following. If the 

 subject be restless or uneasy during the night, so that bedding is 

 removed, the correction is of course affected, and such condition must 

 be considered in applying the correction. 



This correction applies only to the measurements of heat for different 

 periods of the day. For the whole day the two corrections are com- 

 pensating and are therefore negligible. 



CORRECTION FOR CHANGE OF BODY TEMPERATURE AND BODY WEIGHT. 



In the calculations thus far outlined it has been assumed that the 

 temperature of the body of the subject has been constant throughout 

 an entire period, and that there has been no gain or loss of body weight. 

 It is obvious, however, that in an actual experiment either or both of 

 these assumptions may be incorrect. Accurate temperature measure- 

 ments show a considerable variation even under apparently uniform 

 conditions, and the body weight undergoes a continual loss through the 

 elimination of body carbon and hydrogen as carbon dioxide and water 

 vapor by the lungs and skin, besides the marked gains and losses fol- 

 lowing the intake of food and the excretion of feces and urine. 



The effect of such fluctuations may be that of either increasing or 

 decreasing the amount of heat measured during the period. Thus, if 

 the body weight has remained constant, but the body temperature has 

 increased, there has been an absorption of heat by the body which has 

 escaped measurement. An amount equivalent to the gain in temper- 

 ature multiplied by the body weight and the specific heat of the body 

 is therefore to be added. On the other hand, a fall in temperature 

 would give a correction to be subtracted. Similarly, if the temperature 

 remains constant, a gain in weight denotes a correction to be added to 

 the heat measured, since with this gain of weight a certain amount of 

 heat, depending upon the specific heat of the substance gained and the 

 difference in temperature of the body and the chamber, has been 

 required to raise the substance from the temperature of the chamber to 

 that of the body. In case both body temperature and body weight 

 have varied, the correction may be either positive or negative. 



In practice, readings of body temperature are taken, when practi- 

 cable every four minutes, and arrangements are such as to permit of 

 weighing the subject at the end of each period if desired. The neces- 

 sary corrections may then be applied. 



