194 A N I M A L H E A T. 



circumstances, hardly discernible. Among these lower ani- 

 mals, however, the observations of Mr. Newport supply con- 

 firmatory evidence. He shows that the larva, in which the 

 respiratory organs are smaller in comparison with the size of 

 the body, has a lower temperature than the perfect insect. 

 Volant insects have the highest temperature, and they have 

 always the largest respiratory organs and breathe the greatest 

 quantity of air; while among terrestrial insects, those also 

 produce the most heat which have the largest respiratory or- 

 gans and breathe the most air. During sleep, hibernation, 

 and other states of inaction, respiration is slower or suspended, 

 and the temperature is proportionately diminished ; while, on 

 the other hand, when the insect is most active and respiring 

 most voluminously, its amount of temperature is at its maxi- 

 mum, and corresponds with the quantity of respiration. 

 Neither the rapidity of the circulation, nor the size of the 

 nervous system, according to Mr. Newport, presents such a 

 constant relation to the evolution of heat. 



On the Regulation of the Temperature of the Human Body. 



The continual production of heat in the body has been 

 already referred to. There is also, of necessity, a continual 

 loss. But in healthy, warm-blooded animals, as already re- 

 marked, the loss and gain of heat are so nearly balanced one 

 by the other, that under all ordinary circumstances, a uni- 

 form temperature, within two or three degrees, is preserved. 



The loss of heat from the human body takes place chiefly 

 by radiation and conduction from its surface, and by means 

 of the constant evaporation of water from the same part, and 

 from the air-passages. In each act of respiration, heat is also 

 lost by so much warmth as the expired air acquires (p. 173). 

 All food and drink which enter the body at a lower tempera- 

 ture than itself, abstract a small measure of heat, and the 

 urine and faeces take about a like amount away, when they 

 leave the body. Lastly, some part of the heat of the body is 

 rendered imperceptible, and therefore lost as heat, by being 

 manifested in the form of mechanical motion. 



By far the most important loss of heat from the body, 

 probably 80 or 90 per cent, of the whole amount, is that 

 which proceeds from radiation, conduction, and evaporation 

 from the skin. And it is to this part especially, and in a 

 smaller measure to the air-passages, that we must look for the 

 means by which the temperature is regulated ; in other words, 

 by which it is prevented from rising beyond the normal point 

 on the one hand, or sinking below it on the other. The chief 



