2l8 NUTRITION OF FARM ANIMALS 



inferred, as in the case of the falling body or the pendulum, that 

 the kinetic energy produced has been derived from some other 

 form of energy. In the examples thus far given this other form 

 of energy was gravitation energy. In many familiar instances, 

 however, this is not the case. The expanding steam in the 

 cylinder of a steam engine parts with some of its heat to produce 

 the motion of the piston. The electric current in the wire sets 

 the armature of the motor in revolution. The combustion of 

 gasoline in the cylinder of an engine produces motion of the 

 engine as well as heat. Heat, electricity and chemical action 

 may all be sources of kinetic energy and therefore the existence 

 of heat energy, electrical energy and chemical energy is inferred. 

 The manifestations of energy are of the most varied charac- 

 ter but its forms may be conveniently grouped under the fol- 

 lowing general heads : 



1. Kinetic energy 6. Magnetic energy 



2. Gravitation energy 7. Chemical energy 



3. Cohesion energy 8. Heat energy 



4. Volume energy 9. Radiant energy 



5. Electrical energy 



Of these, kinetic energy, chemical energy and heat energy 

 are those of most importance in considering the balance of en- 

 ergy in the animal body. 



305. Transformations of energy. As is illustrated by the 

 examples given in the previous paragraphs, and as has been 

 assumed in speaking of energy changes in the animal body, the 

 various forms of energy are capable of mutual transformations. 

 Heat may be converted into motion in the heat engine. Motion 

 in turn is converted into heat when a moving body is retarded 

 by friction or stopped by contact with another body. When 

 gasoline is burned freely, its chemical energy is converted into 

 heat, but when it is exploded in the cylinder of an engine it 

 yields also motion. This motion in turn may be stored in the 

 form of gravitation energy in a lifted weight, or as cohesion 

 energy in a coiled spring, or it may be made a source of elec- 

 trical-energy which in its turn gives rise to the radiant energy 

 of light in the filament of a lamp. 



In brief, all the physical phenomena of the universe of which 

 we can take cognizance can be described in terms of changes of 



