302 physiological regulations 



§ 112. Maintenance in man 



The recognition of constancy of heat content of the human body 

 is almost universal. Perhaps this content is measured, as body 

 temperature, oftener than content of any other component. 



How are heat exchanges related to heat content? This might 

 be answered by procedures familiar in the study of air-conditioning 

 of a house. Observations of the thermostatic arrangements are 

 alone not sufficient ; the behavior of the installed apparatus in the 

 house must be examined. The whole house would itself be exposed 

 to diverse external conditions when performance is being de- 

 scribed. In the human body a similar study is a desirable pre- 

 liminary to characterizing a state of fever, of hypothalamic lesion, 

 or of heat stroke. 



That heat gain in the long run equals heat loss may be regarded 

 as a prediction of the first and second "laws" of energy. None 

 the less, it was accepted as a singular victory for thermodynamics 

 whenEubner (1894) in the dog, and Atwater (see Lusk, '33, p. 120) 

 in man, ascertained that the oxygen consumed and the carbon diox- 

 ide produced in 24 hours of metabolic transformations actually 

 yield energy equivalent to the amount of heat collected in a 

 calorimeter. 



The known course of energy transfer predicts that heat is 

 scarcely transformed into any other kind of energy without the 

 presence of large differences of temperature. Of all forms of 

 energy, therefore, the chances of completely measuring heat output 

 are greater than of measuring other outputs. Turnover of heat in 

 man amounts to about 1 Cal./kg. hr. in usual circumstances. 

 Further, a huge number of factors have been identified as having 

 some influence upon it. 



The balanced state of the body is any one in which rate of heat 

 gain equals rate of heat loss. Though the actual heat content of 

 the body might be unusual, rates of both total exchanges are then 

 correspondingly greater than basal ones, and an unusual balance 

 prevails. Hence it is possible to distinguish a usual balance from 

 others. 



Usual balances are characterized by the presence of those rectal 

 or oral temperatures found in a random population. The varia- 

 bilities of these temperatures at a uniform time of day in a given 

 set of conditions (table 33) are indicated by standard deviations, 



