CHAPTER X 

 PERIODIC FLUCTUATIONS IN BODY TEMPERATURE 



Homoiotlierms may show periodic fluctuations, di- 

 urnal or seasonal, in body temperature while in a state 

 of normal health. They may also show variations in 

 body temperature which are independent of extracorpo- 

 ral or periodically recurring influences during certain 

 phases of their life cycle. No intrinsic periodic fluctua- 

 tions are apparent in the poikilotherms, obviously be- 

 cause the environmental temperature is the determining 

 factor. 



Diurnal Variation. — The diurnal variation in the 

 normal body temperature of animals has been little 

 studied. In man its usual range is about 1 deg. C. The 

 maximum temperature usually occurs about 4 to 6 p. m. 

 and the minimum about 4 to 6 a. m. With these diurnal 

 changes in temperature are associated parallel oscilla- 

 tions in the rate of metabolism, as shown by the elimi- 

 nation of carbon dioxide. While such variation may be 

 partially accounted for by the movement and tonus of the 

 muscles occurring during the waking hours, an inherent 

 cycle apparently exists. Benedict's (1904) observations 

 made on night workers showed that adjustment to change 

 in the daily routine was incomplete even after a period 

 of years. Gibson (1905) found that his diurnal metabolic 

 variations maintained a parallelism with the daylight 

 and darkness while he traveled around the world. It 



79 



