444 TEXT-BOOK OF PHYSIOLOGY 



Variations in the Mean Temperature. The mean temperature of 

 the human body for twenty-four hours, which for the mouth and the rec- 

 tum may be accepted at 36.8C. and 37.2C. respectively, is subject to 

 variations from a variety of circumstances, such as age, periods of the day, 

 food, exercise, etc. 



Age. At birth the temperature of the infant is slightly higher than 

 that of the mother, registering in the rectum about 37.5C. In a few hours 

 it rapidly declines to about 36.5, to be followed in the course of twenty-four 

 hours by a rise to the normal or slightly beyond. During childhood the 

 temperature gradually approximates that of the adult. In old age the tem- 

 perature rises, as a rule, and attains a maximum at eighty years of 37.4C. 



Periods of the Day. The observations of Jiirgensen show that there is 

 a diurnal variation in the mean temperature of from o.5C. to i.5C., the 

 maximum occurring late in the afternoon, from 5 to 7 o'clock, the minim am 

 early in the morning, from 4 to 7 o'clock. This diurnal variation in 

 the mean temperature is related to corresponding variations in many other 

 physiologic processes, and its causes are to be found in the ordinary habits 

 of life as regards the time of meals, periods of exercise, sleep, etc. 



Food and Drink. The ingestion of a hearty meal increases the tempera- 

 ture but slightly not more than o.5C. Insufficiency of food lowers 

 the temperature; total withdrawal of food, as in starvation, is followed by 

 a steady though slight decline, until just preceding the death of the animal, 

 when it falls abruptly to from 6 to 8C. Cold drinks lower, hot drinks 

 raise the temperature. Food and drinks, however, only temporarily 

 change the mean temperature, and after a short period equilibrium is re- 

 stored through the activity of the heat-regulating mechanism. Alcoholic 

 drinks lower the temperature about o.5C. In large toxic doses in persons 

 unaccustomed to their use the temperature may be lowered several degrees. 

 This is attributed not to a diminution in heat-production, but rather to an 

 increase in heat-dissipation (Reichert) from increased action of the heart, 

 dilatation of the blood-vessels of the skin, and increased activity of the 

 sweat-glands. 



Exercise. The temperature may be raised by active muscular exercise 

 from i to i.5C. as a result of increased activity in chemic changes in the 

 muscles themselves. A rise beyond this point is prevented by the in- 

 creased activity of the circulatory apparatus, the removal of the heat to the 

 surface, and its rapid radiation. 



External Temperature. The external temperature influences but slightly 

 the mean temperature of the human body. In the tropic, as well as in the 

 arctic regions, notwithstanding the change in the temperature of the air, 

 the temperature of the body remains almost constant. The same is true 

 for the seasonal variations in the temperature of the temperate regions. 



The Residual Heat of the Body. As a preliminary to a consideration 

 of heat-production and heat-dissipation, it is of interest to determine the 

 actual quantity of heat expressed in Calories, that resides in the body at all 

 times. This can be approximately determined from the chemic composi- 

 tion and the temperature . A chemic analysis of the body shows that it con- 

 sists of water 0.6, and of tissue 0.4. If the weight be assumed to be 70 

 kilograms then 42 kilograms consist of water, and as the temperature is 

 37C., the 42 kilos of water will contain 42 X 37 or 1554 kilogram calories; 



