ANIMAL HEAT. 387 



/Tl 



lere is thus usually a difference between the two sides of the heart 

 of about 0.2 C. s, 



Variations m the Mean Temperature. The mean tempera- 

 ture of the human body for twenty-four hours, which for the mouth 

 and rectum may be accepted at 36.7 C. and 7-2 C. 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 37.5 C. 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 temperature rises, as a rule, and attains a 

 maximum at eighty years of 37.4 C. 



Periods of the Day. The observations of Jlirgensen show that 

 there is a diurnal variation in the mean temperature of from 0.5 C. 

 to 1.5 C., the maximum occurring late in the afternoon, from 5 to 7 

 o'clock, the minimum 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 

 temperature but slightly not more than 0.5 C. Insufficiency of 

 food lowers the temperature; total withdrawal of food, as in starva- 

 tion, is followed by a steady though slight decline, until just preceding 

 the death of the animal, when it falls abruptly to from 6 to 8 C. 

 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 restored through the activity 

 of the heat-regulating mechanism. ^Alcoholic drinks Inw&r the tem- 

 perature about 0.5 C.j* 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. Tne temperature may beraised by active muscular 

 exercise from i to 1.5 C. as a result of increased activity in 

 chemicTchanges in the muscles themselves. A ris^foyfflKf this point 

 is prevented by the increased activity of the circulatory apparatus, 

 the removal "oTthe 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 



