52 APPLIED PHYSIOLOGY 



molecules of human cells ' dance ' most actively. If the 

 temperature of the body falls below this point, their 

 movements become more sluggish; whilst if it rises 

 much above this point, they may dance more violently 

 indeed, but it tends to be a dance of death. Of the two 

 extremes, a low temperature would appear to be the 

 less dangerous, for whilst clinical observation shows 

 that recovery may ensue even when the temperature of 

 the body has fallen as low as 75 F., a rise of even 

 13i F. above the normal is but rarely survived unless it 

 be of short duration. 



Although the heat-regulating mechanism succeeds in 

 keeping the mean temperature of the body very uniform, 

 slight daily variations do occur, the maximum being 

 reached about five o'clock in the evening, and the 

 minimum in the small hours of the morning. In cases 

 of fever these normal variations are sometimes exag- 

 gerated, and a * two-hourly ' chart may therefore exhibit 

 a rise of temperature which would be missed if the 

 thermometer is used only twice a day. The cause of 

 these daily variations is obscure, but it is certain that 

 they occur during both starvation and complete rest, 

 and it is probable that they result from the normal 

 daily fluctuations in metabolism to which reference has 

 already been made (p. 20). In people who pursue 

 nocturnal vocations the daily rhythm of temperature 

 may be inverted, the maximum being attained in the 

 early morning, and the minimum in the evening. So 

 stereotyped, however, has the normal type of meta- 

 bolism become through long habit that such inversions 

 of it are but rarely met with. 



