CHAPTER 10 



INTRODUCTION 



Temperature: Metabolic Aspects and Perception 



T 



■ EMPERATURE, PERHAPS MORE than Other environmental tactors, has 

 I multiple and diverse effects on living organisms. Temperature is 

 B a measure of molecular agitation; it limits the rate of chemical 

 reactions; hence it determines growth and metaKolism in the widest sense. 

 Temperature limits the survival and the distribution of animals on the earth. 

 The cell temperature limits for active life are from about to about +45° C, 

 and many higher animals die within still narrower limits. 



Many animals respond to changes in environmental temperature by con- 

 forming passively to the environment; these are the cold-blooded or poikilo- 

 thermic animals. A poikilothermic animal can protect itself against unfavor- 

 able temperatures by entering a protective state of dormancy or encystment, or 

 by going to a region of more favorable temperature. Comparatively few ani- 

 mals regulate their body temperature; these are the warm-blooded or homoio- 

 thermic animals. Heterothermic animals are those with limited temperature 

 regulation. Warm-blooded animals can react to temperature extremes by pro- 

 tective behavior, and in addition they can alter heat loss by varying their 

 insulation and can alter heat production by varying their metabolism. Sensory 

 mechanisms signal the changes in temperature which evoke the various pro- 

 tective responses. 



The temperature of any metabolizing cell is necessarily higher than the 

 temperature of its medium, because oxidation and glycolysis liberate heat. 

 The temperature of an animal depends on the balance of those factors which 

 tend to add heat and those which tend to subtract heat: 



Factors Which Cause Addition of Heat 



oxidative and other metabolic 

 production of heat 



absorption of heat, largely from 

 solar radiation 



Factors Which Cause Loss of Heat 

 radiation 



conduction and convection 

 vaporization of water 

 circulation of heat from interior to surface 



The measurement ot temperature is so easy, by mercury thermometer or 

 thermocouple, that the literature on temperature relations is vast. Various 

 aspects have been summarized by numerous authors. ^^' ^^'' •^''■' ''■' 



THERMAL PROPERTIES OF WATER 



The temperature relations of animals to their environment are closely 

 connected with their water relations. The thermal properties of water are 



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