ANIMAL HEAT. 63 



ternal organs the thermometer may indicate as high as 100 F. in 

 normal conditions. In the rectum the temperature is about 1 F. 

 higher than in mouth or armpit. 



Is this normal temperature constantly maintained? 



Yes. with very trifling variations. Under all circumstances the 

 healthy body maintains about this temperature, varying very 

 slightly under torrid and frigid climates. There are also slight 

 variations from exercise, age, etc. 



How is this heat maintained? 



It is produced from union of the oxygen of the air, which is 

 taken up by the blood in the lungs, with carbon and hydrogen. 

 This is an exact analogy of combustion in the air. 



What products result from this combustion in the body ? 

 Carbonic oxide and water. 



What is metabolism? 



It is a change constantly going on in the body by which the 

 protoplasm of cells is destroyed in doing work (destructive metab- 

 olism), and by which new protoplasm is built up by the assimi- 

 lation of food (constructive metabolism). When any group of 

 cells is in active use (c. g. in a muscle) the destructive process 

 is rapid and the formation of carbonic oxide and water is active ; 

 in other words, there is active combustion of the cells with the 

 production of heat. Simultaneously, there is reconstruction of 

 the used protoplasm, but this prpcess is not accompanied by the 

 creation of heat. 



How is the loss of heat regulated ? 



(1) The blood at the surface of the body is cooled by the colder 

 air or by evaporation of the sweat. This is automatically regulated 

 by the vaso-motor nerves, for upon exposure to a colder atmosphere 

 there is immediate contraction of the superficial capillaries, and upon 

 entering a warmer environment there is dilatation ; so that the quan- 

 tity of blood presented for cooling is an inconstant factor, depending 

 upon external temperature. The sweat-production is similarly under 

 reflex control. 



(2) Loss of heat is considerable by the lungs, though less than 

 that from the skin : the air is warmer, in usual conditions, after 

 leaving the lungs than before it has entered them. 



