ANIMAL HEAT. 135 



ANIMAL HEAT. 



The functional activity of all the organs and tissues of the body is 

 attended by the evolution of heat, which is independent, for the most part, 

 of external conditions. Heat is a necessary condition for the due performance 

 of all vital actions; although the body constantly loses heat by radiation and 

 evaporation, it possesses the capability of renewing it and of maintaining it at 

 a fixed standard. The normal temperature of the body in the adult, as shown 

 by means of a delicate thermometer placed in the axilla, ranges from 97.25 

 F. to 99.5 F., though the mean normal temperature is estimated by Wunder- 

 lich at 98.6 F. 



The temperature varies in different portions of the body according to 

 the extent to which oxidation takes place, being highest in the muscles, in 

 the brain, blood, liver, etc. 



The conditions which produce variations in the normal temperature 

 of the body are: age, period of the day, exercise, food and drink, climate, 

 season, and disease. 



Age. At birth the temperature of the infant is about i F. above that 

 of the adult, but in a few hours falls to 95.5 F., to be followed in the course 

 of twenty-four hours by a rise to the normal or a degree beyond. During 

 childhood the temperature approaches that of the adult; in aged persons 

 the temperature remains about the same, though they are not so capable of 

 resisting the depressing effects of external cold as adults. A diurnal variation 

 of the temperature occurs from i .8 F. to 3.7 F. (Jiirgenseri); the maximum 

 occurring late in the afternoon, from 4 to 9 P. M. ; the minimum, early in the 

 morning, from I to 7 A. M. 



Exercise. The temperature is raised from i to 2 F. during active con- 

 tractions of the muscular masses, and is probably due to the increased 

 activity of chemic changes; a rise beyond this point being prevented by its 

 diffusion to the surface, consequent on a more rapid circulation, radiation, 

 more rapid breathing, etc. 



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

 ture but slightly; an absence of food, as in starvation, produces a marked 

 decrease. Alcoholic drinks, in large amounts, in persons unaccustomed to 

 their use, cause a depression of the temperature amounting to from i to 2 

 F. Tea causes a slight elevation. 



External Temperature. Long-continued exposure to cold, especially if 

 the body is at rest, diminishes the temperature from i to 2 F., while exposure 

 to a great heat slightly increases it. 



Disease frequently causes a marked variation in the normal temperature 

 of the body, which rises as high as 107 F. in typhoid fever and 105 F. in 



