CONTENTS. XI 



ou the principle of the lever standing mechanical contriv- 

 ances in the leg of Birds walking leaping running. -influ- 

 ence of education on the muscles gymnastic exe.cises. . . . 197 



CONVERSATION IX. 



Sleep necessary quantity varied by habit, age, and temperament 

 state of the brain during sleep dreaming somnambulism 

 influence of sleep on the other functions influence of bsbit on 

 the animal and organic functions difference of origin relations 

 and mutual influence of the functions laws of coexistence 

 death. . . 227 



