CHANGES OF LIFELESS AND LIVING MATTER 9 



complex substances, and in their bodies there are constant 

 physical and chemical changes connected with all life-activi- 

 ties. Especially do foods eaten and oxygen from the breathed 

 air become involved in numerous changes in the living 

 matter of animal and plant bodies. Many times in later 

 lessons we shall need to refer to the principles of chemistry 

 and physics which this chapter reviews. 



Summary : (1) Both living and lifeless matter may un- 

 dergo physical and chemical changes; and (2) all matter is 

 composed of elements, usually combined in compounds, and 

 capable under certain conditions of new recombinations into 

 other compounds. 



