FUNCTIONS OF THE NERVOUS SYSTEM 309 



A fish under similar conditions will continue to swim 

 in a straight line unless obstacles appear, and those it 

 will avoid as usual. Its movement will be kept up until 

 ended by exhaustion. It will never pause to eat, though 

 abundance is on every side. Like the frog, the fish de- 

 prived of its cerebrum is incapable of any action not the 

 result of immediate and direct external stimulus. It 

 swims because the contact of the water with the surface 

 furnishes constant irritation to the swimming mechanism. 

 Corresponding results follow experiments upon higher 

 animals and observations upon man himself. The lower 

 nerve centers act at once in response to present stimulus, 

 and act without necessarily affecting consciousness, with- 

 out sensation, and without will. 



451. The frog or the fish retaining the whole of the 

 brain intact responds to external irritation, but the pre- 

 cise results of such irritation cannot be accurately pre- 

 dicted, and the action may be deferred for a longer time 

 than when the cerebrum is wanting. 



In the higher animals the varieties of possible results 

 of stimulation are still more numerous. Strike a wild 

 cat over the nose with a club and he may turn and flee, 

 or he may plunge forward and bury his teeth in your 

 body. The nervous discharge in all these cases will, 

 however, be likely to take place with considerable prompt- 

 ness in one way or another. 



But suppose a man to receive a severe injury or insult. 

 He may retaliate at once by shooting or knocking down 

 his assailant, or he may cherish a sense of wrong for many 

 years, seeking opportunity for revenge. He may even 

 inculcate the enmity upon the minds of his* children, to be 

 passed on from generation to generation as a family feud. 

 In man, therefore, and to some extent in the higher ani- 



