lO ELEMENTARY BIOLOGY 



changed into spme other. Chemical energy and X-rays and 

 'motion are other forms of energy. 



• . We may tliink'Df energy as that wliicli brings about changes 

 in matter,, or that which does work. 



,14. Energy and matter. If we fix our attention upon any 

 happening or change, we can see that matter undergoes some 

 change, and that at the same time energy undergoes some 

 change. Moreover, we can see that whatever happens has not 

 only been started by some previous change, but also starts; 

 some other changes in its turn. Thus we may get the idea 

 not only that energy causes changes in matter, but also that 

 matter causes changes in energy. One statement is just as true 

 as the other. We may get the further idea that every event is 

 a link in an endless chain of events, and that these many links 

 may connect up in every possible direction. 



15. Conservation of energy. One kind of energy can be 

 converted into other kinds of energy, but the total amount of 

 energy always remains the same. There is no way of getting 

 energy except from other energy. Energy, like matte?; caji 

 neither be er^eated nor destroyed. 



