ANIMAL HEAT. 485 



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 influence of age is shown by the fact that 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. 430), 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 sjiecies, 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- 

 pation is greater when the animal is in the water than when exposed to the air 

 if both water and air be of the same temperature, because water is a better 

 conductor of heat and consequently withdraws heat from the body more 

 rapidly. The higher the temperature of the surroundings the higher the 

 bodily temperature of cold-blooded animals, consequently the greater are heat- 

 production and heat-dissipation. In warm-blooded animals the effect on both 

 heat-production and heat-dissipation is in inverse relation to the surrounding 

 temperature (unless the bodily temperature is affected), external heat decreasing 

 both heat-dissipation and heat-production, and internal heat increasing both. 



Subcutaneous fat is a poor conductor of heat, consequently the greater the 

 abundance of it the greater the hindrance offered to the dissipation of heat. 

 The value of fat in this respect is illustrated in water-fowls, which, as a rule, 

 are far more abundantly supplied with fat than other species; and by the ex- 

 ceptional abundance of subcutaneous fat in species of fowl which inhabit very 

 cold waters. Bathing the skin with grease hinders radiation, and is adopted 

 by swimmers both to conserve the bodily heat and to protect the skin. 



When air and water are of the same temperature, heat-dissipation is greater 

 when the animal is exposed to the water, because the latter is abetter con- 

 ductor. Heat-loss is greater in dry than in moist air, other things being 



