430 MANUAL OF PHYSIOLOGY. 



fasting. During starvation the temperature sinks gradually until 

 the death of the individual. 



c. The temperature is highest at birth, and falls about 1 C. 

 between that and the age of 50 years in extreme old age it is 

 said that it again rises. 



d. Muscular exertion, which gives the individual the sensation 

 of great warmth, only changes the temperature of the blood about 

 .5 C. The very high temperature which accompanies the disease 

 Tetanus, where all the muscles are thrown into a state of spasm, 

 probably depends more on pathological changes than on muscular 

 action. 



e. Mental exertion is also said to cause a rise of temperature. 

 /. Slight differences in the heat of the blood may be brought 



about by variations in the surrounding temperature. The abnor- 

 mally high temperature of fever is much more easily affected by 

 changes in the rate of removal of the heat from the body than is 

 the normal temperature, and hence the therapeutic value of cold 

 applications in this class of diseases. 



II. The temperature of different parts of the body varies in a 

 slight degree, and depends upon the following circumstances : 1. 

 The amount of blood flowing through them ; for the blood is the 

 great carrier of warmth from one part to another, supplying 

 heat where it is lost by exposure, etc., and it conveys material 

 to those parts where the heat is generated. 2. The amount of 

 heat produced in a given part, i. e, the activity of its tissue 

 change. 3. The amount of heat lost, which depends on (a) the 

 extent of surface ; (b) the external temperature ; (c) the power 

 of conduction of, and the capacity for heat of, the surrounding 

 medium. 



From this it is obvious that the deeper parts of the body, where 

 active chemical change takes place and which are protected from 

 exposure, must be warmer than the exterior, which is constantly 

 losing its heat to the air. The blood, then, which flows through 

 the surface vessels is cooled, and that which flows through the 

 deeper vascular viscera is warmed. Thus the skin is usually about 

 37 C., while the mouth beneath the tongue is about 37.5 C., 

 and the rectum about 38 C. Accordingly, then, as the blood has 



