LETTERS TO BROTHER JOHN. 85 



always telling the truth with a grave face ? Why 

 should we not sometimes tell it with a smiling eye, 

 as well as a scowling brow ? Gravity is not wisdom; 

 nor a smile, folly. Besides, if to smile be a folly, 

 what then? " Qui vit sans folie, n'est pas si sage 

 qu'il croit," says Rochefaucauld. 



Organism, then, is that arrangement of the com- 

 ponent parts of matter which fits it to be endowed 

 with contractility and sensibility. Contractility is 

 that property which endows it with the power of 

 executing living motions. Stimuli are impressing 

 causes, acting on its contractility, and exciting it 

 (organized matter) to action ; and sensibility is the 

 property by which it perceives the presence of these 

 impressing causes. 



The muscles of your arm are organized, and they 

 possess contractility and sensibility; and when you 

 resolve to raise your arm, your will becomes an 

 impressing cause, exciting those muscles to action ; 

 that is, to contract. Their sensibility makes them 

 aware that this impressing cause, or stimulus, (viz. 

 the will,) is acting upon them; and they contract in 

 obedience to it ; and your arm is raised accordingly. 



But if the nerves, which convey that stimulus 

 from the brain to the arm, be paralyzed, you may 

 will "till the crack of doom"; your arm will not 



