44 ELEMENTARY ZOOLOGY. 



6. Justify the statement that irritability of proto- 

 plasm is at the foundation of all the life activities. 



7. Why are the chemically complex organic substances 

 likely to be unstable? Why does this fit them to be used 

 as foods? 



57. Words to be derived and defined. 



Organized; protoplasm; assimilation; instability; stim- 

 ulus; oxidation; chemical element; chemical compound. 



