606 A MANUAL OF PHYSIOLOGY 



maximum and minimum fall at the same periods ; and it is of 

 scientific, and also of practical, interest that the early morning, 

 when the temperature and pulse-rate are at their minimum, is 

 often the time at which the nagging powers of the sick give way. 

 From two to six o'clock in the morning the daily tide of life 

 may be said to reach low-water mark. Even in a fasting man 

 the diurnal temperature curve runs its course, but the varia- 

 tions are not so great. The taking of food of itself causes an 

 increase of temperature, although in a healthy man this rarely 

 amounts to more than half a degree. The rise of temperature 

 is certainly due in part to the increased work of the alimentary 

 canal, but it is also connected with the increase of metabolic 

 activity which the entrance of the products of digestion into the 

 blood brings about. The heat-production is especially increased 



by proteins. The rise of 

 temperature during di- 

 gestion is gradual, the 

 maximum being reached 

 during the fourth hour, 

 or even later. The great- 

 est increase of heat-pro- 

 duction takes place during 

 the first hour after feeding 

 (Reichert). 



The cause of the daily 

 variation of temperature 

 has been much discussed. 

 There is no doubt that 

 several factors are con- 



FlG. 200.-CURVE SHOWING THE DAILY cemed among the most 



VARIATION OF BODY-TEMPERATURE. . & 



important being the vari- 

 ation in the amount of contraction of the skeletal muscles 

 and the influence of food. Muscular exercise is capable of 

 causing a considerable rise in the temperature of the rectum 

 and urine, to 38-5 C. (101-3 F.) or even 38-9 C. (102 F.) 

 without producing any feeling of distress. Other unknown 

 influences seem also to be involved, as is shown by the fact 

 that in persons who work at night and sleep during the 

 day the curve of temperature, although greatly altered, is 

 not reversed. Recent observations on this subject are those 

 of Benedict. By means of a resistance thermometer in the 

 rectum, readings were taken usually every four minutes. With 

 such a thermometer no disturbance of the person's sleep is 

 necessary to obtain a reading. He can sit without discomfort 

 in any position, walk about the room (returning to the observer's 

 table for the observations), and even ride a stationary bicycle. 

 Even years of night-work do not eliminate the tendency to a 



