190 Metabolism of Healthy Man. 



certain discrepancies in the results that make it impossible to accept the 2-hour 

 figures for each experiment by itself. Thus, in the 4 successive 2-hour periods 

 from 11 p. m. to 7 a. m., the heat production was 71.5, 65, 60.9, and 46.3 

 calories per hour, respectively, for each 2-hour period. For the period from 

 7 a. m. to 9 a. m., the heat production rose again to 69.4 calories. It is evident 

 that the extremely low value observed in the period from 5 a. m. to 7 a. m. 

 does not strictly represent the heat production during this time. While, there- 

 fore, the result for the 22 hours probably represents with considerable accuracy 

 the true heat production of this subject, no very sharp distinction can be made 

 between the hours when the subject was awake and when she was asleep, and, 

 unfortunately, some of the results can not be used intelligently in discussing 

 this relationship. 



Heat Production as Compared with Heat Elimination. 



The measurement of the heat radiated and conducted from the surface of 

 the body, the heat required to vaporize the water from the lungs and skin, 

 and the sensible heat of excreta do not give by any means a true measurement 

 of the heat production during a given period. There is a large reservoir of 

 heat, as it were, in the body itself, and if there is a material change in body- 

 temperature there is a material difference in the amount of heat stored in the 

 body. If there is a rise in body-temperature, heat has been required to warm 

 the body, and if there is a fall in temperature, some of the heat previously 

 stored has been liberated. From the specific heat of the body and the weight 

 of body-material, it is seen that the capacity of the body for storing heat is 

 very great. It has been commonly assumed that the specific heat of the body 

 is 0.83, and for a man of average body-weight, say 60 kilos, it can be seen that 

 the hydrothermal equivalent of the body is practically 50 kilos. Consequently, 

 if the body-temperature is increased 1, this is equivalent to the storage of 

 50 calories of heat. A tenth of a degree change, which is relatively common, 

 corresponds to 5 or 6 calories. Conversely, if the body-temperature falls, the 

 equivalent amount of heat has been lost from the body, and measured by the 

 apparatus, together with the heat produced during that period, and the measured 

 heat is therefore greater than the heat produced by the amount of heat lost 

 from the body in the process of cooling. 



In experiments of 24 hours or more, these fluctuations in body-temperature 

 do not play any considerable role. In experiments of 2 hours, or in subdividing 

 24-hour experiments into 2-hour periods, the true heat production measured 

 for periods as short as 2 hours may be very considerably vitiated by neglecting 

 to take into consideration changes in body-temperature and body-weight. We 

 have, therefore, designated as heat elimination the heat as measured by the 

 calorimeter and corrected for the heat of vaporization of water and sensible 

 heat of excreta; and as heat production, the heat elimination corrected for 

 changes in body-temperature and body- weight. As will be seen, the heat elim- 



