HOMOIOTHERMISM 



CHAPTER I 

 INTRODUCTION 



Warm-blooded, or homoiothermie, animals trnqnes- 

 tionably had their origin through evolutionary changes 

 from cold-blooded, or poikilothermic, animals. By ac- 

 quiring the ability to maintain a comparatively constant 

 and high temperature, the former have become more or 

 less independent of temperature changes in the environ- 

 ment. A homoiothermie animal lives at approximately 

 the same rate at all seasons and at all latitudes, but a 

 poikilothermic animal must slow down its life processes 

 whenever its surroundings become cooler. 



Of course warmth is not the cause of metabolism, but 

 is one of the conditions for it. Homoiotherms have 

 gained to some degree the ability to ignore the environ- 

 ment. They have done this by means of certain mechan- 

 isms for heat production, insulation on the outsides of 

 their bodies, the transfer of liquids from certain parts 

 of their bodies to others, and other adaptations. The 

 cells within their bodies live at rather constant tempera- 

 tures which are close to the optimum for metabolic activi- 

 ties. Some poikilotherms which inhabit cold oceans pass 

 their whole lives below deg. C. These animals must 

 live on a lower metabolic and psychic level than such 

 active cold water animals as penguins or whales. On 



