592 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



It is said that heat-production undergoes diurnal variations which corre- 

 spond with the fluctuations of bodily temperature, but this is doubtful. 



All structures produce more heat during activity than during rest. Heat- 

 production has been estimated to be from two and a half to three times greater 

 when awake and resting than when asleep, and from one and a half to three 

 times more when active than when at rest, in proportion to the degree of 

 activity. During hybernation the absorption of O falls considerably (p. 542), 

 consequently heat-production is believed to decline to a like degree. 



All circumstances which affect heat-dissipation (p. 601) tend indirectly to 

 influence heat-production. 



The most important of the factors influencing heat-production is the ner- 

 vous mechanism which controls the heat-producing processes (p. 598). 



Various drugs exert more or less potent influences directly or indirectly upon 

 heat-production. Cocain, strychnin, brucin, and other motor excitants increase 

 heat-production ; while chloroform, most antipyretics, narcotics generally, bro- 

 mides, and motor depressants decrease heat-production. 



Heat-production is diminished in most forms of anaemia, after severe hem- 

 orrhage, and in most non-febrile adynamic conditions. It is usually increased 

 in fevers, especially so in infectious fevers. According to Liebermeister, the 

 increase in fever is probably about 6 per cent, for each increase of 1 C. of 

 bodily temperature, so that were the increase of temperature 3 C. the increase 

 of heat-production would be 18 per cent. 



Conditions affecting- Heat-dissipation. The loss of heat from the body 

 occurs through several channels in the urine, feces, sweat, and expired air, 

 and by radiation and conduction from the skin ; hence, all conditions which 

 affect the loss of heat in the above ways must influence heat-dissipation. The 

 chief of these are : Age, sex, species, the quantity of subcutaneous fat, the 

 nature of the surrounding medium, clothing, internal and external tempera- 

 ture, activity of heat-production, body-surface, the condition of the circulation, 

 respiration, sweat, activity, radiating coefficient, nervous influences, drugs, and 

 abnormal conditions. 



The young dissipate and produce more heat in proportion to body-weight 

 than the adult, this being due chiefly to the relatively greater metabolic 

 activity and the larger proportional body-surface (p. 538), and consequent 

 greater radiation, in the young. 



Sex per se does not seem to exert any influence, although the adult human 

 female, weight for weight and for an equivalent bodily surface, probably dissi- 

 pates less heat than the male, because of her relative abundance of subcu- 

 taneous fat, which hinders heat-dissipation. No difference so far as sex is 

 concerned has been noted in the lower animals. 



Heat-dissipation varies greatly in different species, owing chiefly to relative 

 size and respiratory activity, to the nature of the medium in which the animal 

 lives, and to the character of the body-covering. Heat-dissipation is more 

 active in homothermous animals than in poikilothermous animals, because of 

 the greater activity in the former of heat-production. In amphibia heat-dissi- 



