LIVING MATTER 13 



A Question Simplified. — If we understand how the 

 starch grains are made and how they get into the cells 

 of the potato it will simplify the attempt to explain 

 similar processes in the human body. Starch is manu- 

 factured inside the plant of water and carbon dioxide. 

 The water enters the plant through its roots, the carbon 

 dioxide through its leaves. Hoav % We may consider 

 the root and the leaf as more or less hollow structures 

 covered with a thin, moist membrane. The membrane 

 is a solid, the water is a liquid, and the carbon dioxide 

 is a gas. How do a gas and a liquid pass through a 

 solid ? In order to explain this, we must know some- 

 thing about the nature of a gas, a liquid, and a solid. 



Matter. — Every substance, everything in the world 

 that can be called matter, is made of very tiny particles. 

 These little particles are constantly rotating, or vibrat- 

 ing very rapidly, and they have more or less power to 

 move away from each other. 



If they move very slightly so that they do not change 

 their relative positions, the substance has a definite 

 shape and a definite volume and we call it a solid. If 

 they move freely but not entirely away from each other 

 the substance has a definite volume but no definite shape 

 and we call it a liquid. If their motion is unrestricted 

 so that they may fly entirely away from each other the 

 substance has neither definite shape nor definite volume 

 and we call it a gas. 



Heat. — The word heat means rapidity of vibration. 

 In response to heat a substance may change from a solid 

 to a liquid, or from a liquid to a gas. As it grows hot its 

 particles move more rapidly and push farther and 



