Introduction 3 



themselves, either one part on another, or the whole body 

 from place to place. The motive power is not from the 

 outside world, but the energy of the movements exists in 

 our bodies themselves. 



Again, our bodies are continually breathing, that is, they 

 take in oxygen from the surrounding air. They take in 

 certain substances known as food, similar to those com- 

 posing the body, which are capable through a process 

 called oxidation, or through other chemical changes, of 

 setting free a certain amount of energy. 



Our bodies are continually making heat and giving it out 

 to surrounding objects, the production and the loss of 

 which are so adjusted that the whole body is warm, that is, 

 of a temperature which is higher as a whole than that of 

 surrounding objects. 



Finally, our bodies are continually getting rid of so-called 

 waste-matters, the most important of which are products 

 of the oxidation of the material used as food, or of the 

 substances which make up the organism. 



5. The Main Features that distinguish Living Bodies. 

 The living body, like the dead, is continually losing energy, 

 but unlike the dead body is .by means of food continu- 

 ally restoring its substance and replenishing its stock of 

 energy. A great deal of energy thus stored up in the 

 living body is utilized in doing mechanical work, that is, it is 

 used in performing the various movements of the body. On 

 the other hand, the energy set free in the dead body by 

 oxidation and other chemical changes leaves the body for 

 the most part in the form of heat. We shall learn later on 

 that much of the energy which at last leaves the body as 

 heat exists for a time within the living body in other forms 

 than heat, though eventually transformed into heat. The 

 dead body, left to itself, slowly decays, that is, it slowly 



