THE ALPHABET OF ALL LIVING THINGS 



11 



Live and Dead Engines. A living organism is often compared 

 to a steam engine. Both need a supply of food (fuel), and both 

 must have oxygen to unite with (oxidize) the food and set free 

 its energy. In both, heat is produced by this oxidation and then 

 changed into motion, and in both there are waste products which 

 have to be removed. 



But an engine is only an inorganic thing. It cannot get" its 

 own food, it does not assimilate or grow, it does not excrete its 

 waste products, or reproduce. Really the only way in which it 

 resembles a living thing is that it depends on energy which is 

 released from substances by uniting with oxygen, and turns this 

 energy into motion. 



RESEMBLANCES 



DIFFERENCES 



Similarities based on oxidation, differences based on functions of the 

 protoplasm. 



Other Uses of Oxygen. Oxygen has many other uses in nature. 

 It causes combustion from which we get heat and power. It also 

 causes rusting, oxidation, and decay. Its myriad compounds are 



