'Animals as Motors. 487 



derived from the collision of molecules and atoms, while 

 the gravitation engines use the energy derived from the 

 movement of streams of air or water, traveling as a body. 



ANIMALS AS MOTORS. 



"When animals are viewed from the standpoint of ma- 

 chines they are wonderful mechanisms. Kot only are they 

 self-feeding, self-controlling, self-maintaining and self-re- 

 producing, but they are far more economical in the energy 

 they are able to develop from a given weight of fuel ma- 

 terial, than any other existing form of motor. 



While they are like the steam engine in requiring car- 

 bonaceous fuel, oxygen and water for use in developing 

 energy these are made to combine in the animal body at a 

 much lower temperature than is possible in the steam en- 

 gine, and a much smaller proportion of the fuel value is 

 lost in the form of heat, when work is being done. 



605. The Horse as a Motor. The essential elements 

 which constitute the horse a machine for developing power 

 are (1) a system of rigid levers united by ligaments and 

 capsules at the joints which are automatically lubricated 

 by a synovial fluid; (2) a system of muscles, each one of 

 which is a motor, corresponding in function to the piston 

 and cylinder of a steam engine; (3) a fuel supplying and 



i- removing system, consisting of the digestive, excre- 

 tury arid respiratory organs; (4) a co-ordinating and reg- 

 ulating mechanism, consisting of the nervous system, 

 which throws the different motors or muscles into and out 

 of action at the times needful to secure the results ; ( 5 ) a 

 protecting and insulating system, consisting of the skin 

 and hair, which keeps all of the working parts free from 

 dust and reduces the waste of heat. 



606. Muscles Are Motors. Muscles are made up of bun- 

 dles of fibers which can be stimulated by the nervous sys- 

 tem and made to shorten, thus exerting a pull of greater 

 or less intensity as desired. All muscles do their work by 



