304 PHYSIOLOGICAL REGULATIONS 



in both dogs and men, of about ± 0.20° C. It is well known that a 

 daily cycle shows changes of more than this. If the individual 

 were exposed to random conditions instead of selected ones, greater 

 or smaller variations might be found. In ascertaining a man's 

 body temperature one virtually asks whether his body is keeping 

 within two or three times the standard deviation for the popula- 

 tion. If not, two further questions arise : is he out of balance, or, 

 is he maintaining an unusual (non-basal) balance? Both ques- 

 tions can be answered either by repeated temperature measure- 

 ments that indicate whether net gains or losses of heat are occur- 

 ring, or by complete calorimetry of both heat production and heat 

 loss. It is amazing that few human individuals have been discov- 

 ered who consistently differ in rectal temperature from the mean 

 of all individuals. But the hourly variations in one individual are 

 greater (standard difference ± 0.13 to ± 0.28° C.) in newborns 

 than in adults {± 0.10° C.) (Eaudnitz, 1888). 



It may be noted that in one individual on different days the rate 

 of heat production under ''basal" conditions fluctuates by coeffi- 

 cients of variation of ± 3.5 per cent (table 33). Among individ- 

 uals of one body weight and height the coefficient is ± 2.9 per cent 

 (Berkson and Boothby, '38), values which show that unknown cor- 

 relatives are insignificant in subjects selected as "normal." 



The maintenance of constant heat content may depend upon 

 either (a) continual equality between gain and loss, or (b) succes- 

 sive compensations of one by the other. If gain and loss differ by 

 more than the errors of measurement, within periods of (say) one 

 hour or less, it is natural to ask, which of the exchanges has the 

 more uniform rate, and, does the uniformity of rate indicate a less 

 pliable process? Quantitative answers do not appear to exist for 

 man, but will be given below for rabbit. 



§ 113. Heat loads (Max) 



Departures from the usual balanced state are produced by acci- 

 dental or deliberate changes in body and surroundings. The in- 

 itiation of heat deficits by cold media was systematically studied 

 by Lefevre ('11). A man is placed in a water calorimeter (his p. 

 94) or in a wind calorimeter (p. 103), and the rates of sensible heat 

 loss (non-evaporative loss) are ascertained (table 34). In water, 

 as much as 5.7 Calories/kilogram of body weight are lost in 0.2 

 hour. During the exposure the rate rapidly diminishes until a sta- 



