XII. 



THE EXPKESSION OF THE EMOTIONS IN 

 MAN AND OTHEE ANIMALS. 



The subject is treated under three Principles : thq Prin- 

 ciple of Associated Habit ; the Principle of Antithesis ; 

 and the Principle of the direct action of the nervous 

 system independent of Will and Habit. 



THE PEINCIPLE OF ASSOCIATED HABIT. , ( 



Expression of ^ ^ s notorious how powerful is the foree 

 the Emotions, f habit. The most complex and difficult 

 pa ° e ' movements can in time be performed without 



the least effort or consciousness. It is not positively 

 known how it comes that habit is so efficient in facilitat- 

 ing complex movements ; but physiologists admit that 

 " the conducting power of the nervous fibers increases with 

 the frequency of their excitement." This applies to the 

 nerves of motion and sensation, as well as to those con- 

 nected with the act of thinking. That some physical 

 change is produced in the nerve-cells or nerves which are 

 habitually used can hardly be doubted, for otherwise it is 

 impossible to understand how the tendency to certain ac- 

 quired movements is inherited. 



It is known to every one how difficult or 



even impossible it is, without repeated trials, 



to move the limbs in certain opposed directions which 



