Temperature: Metabolic Aspects and Perception 



373 



cr- 



8000- 



6000 



4 000 



2000 



• CHEEK. POUCH TEMPER.ATUR.E 



• RECTAL TEMPERATURE 

 o O, CONSUMPTION 



4o 



80 



120 



I60 



200 



24o 



280 



MINUTES 



Fig. 99. Average data of waking of three hamsters from hibernation at 4-5° C. O 

 oxygen consumption, (• rectal temperature, • cheek pouch temperature. From Lyman."^ 



CONCLUSIONS 



The abundance and distribution of animals are influenced by temperature 

 in two general respects: life is possible only within certain rather narrow 

 temperature limits, and metabolic activity varies greatly according to tempera- 

 ture. The thermal relations of animals to their environment are closely related 

 to their osmotic relations. 



The normal vital temperature range is based on the thermal properties of 

 water. Natural waters (hot springs excepted), because of their high specific 

 heat and small heat conduction, rarely have a temperature above the upper 

 limits for most aquatic animals— 35 to 40"^ C. At the cold extreme the freezing 

 point of aquatic animals is similar to that of the medium (in marine animals), 

 or lower (in fresh-water animals). The causes of heat and cold death are 

 multiple. Heat death often occurs at temperatures well below those of protein 

 denaturation, and cold death need not involve freezing. Among aquatic poiki- 

 lothermic animals the vital limits are lower for animals acclimatized to a low 

 temperature range than for animals acclimatized to higher temperatures. This 

 must mean that chemical changes occur in the organic substances which are 

 critically affected by extremes of temperature. There are few such striking 

 examples of protoplasmic reorganization as in temperature adjustment. The 

 thermal properties of water protect and at the same time fix the temperature 

 limits of aquatic animals. 



The over-all end of metabolism is the liberation of energy which can be 

 used in mechanical or chemical work or can be lost as heat. If heat production 

 is excessive, heat is lost; if the body temperature of a homoiotherm falls, 

 metaboHsm increases. Poikilotherms have a low basal metabolic rate and they 

 lose so much heat by conduction and convection and by vaporization that they 



