306 ?Hti HUMAN BODY. 



if it be put on its back it will get on its feet; if it be 

 thrown into the air it will fly until it strikes against some- 

 thing on which it can alight; if its feathers be ruffled it 

 will smooth them with its bill. 



The difference between a pigeon in this state and an 

 uninjured pigeon lies in the absence of the power of form- 

 ing ideas or initiating movements. It has no thoughts, no 

 ideas, no Will. We cannot predict what an uninjured 

 pigeon will do under given circumstances: we can say be- 

 forehand what the pigeon with no cerebral hemispheres 

 will do; it is a mere machine or instrument, which can be 

 played upon. In such a pigeon the excitation of any given 

 sensory nerve or nerves excites unconscious nerve-centres 

 which set certain muscles at work, and the result of any 

 one stimulus is always the same invariable movement. 

 The animal exhibits no evidence of possessing any con- 

 sciousness ; it has no desires or emotions ; it is like a piano 

 which while untouched is silent, but when a given key is 

 struck emits always the same note ; so the pigeon without 

 its cerebral hemispheres stays quiet while left to itself, and 

 responds to any one given stimulus always in one invari- 

 able and predicable way. 



Functions of the Cerebellum. The cerebellum is the 

 great centre for co-ordinating the muscles of locomotion. 

 Each step we take implies the action of many muscles and 

 many thousands of muscular fibres; the actions of all must 

 be very precisely graded as to amount, and very accurately 

 arranged as to proper sequence. We do not, however, con- 

 sciously think about the muscles to be used in every move- 

 How does such a pigeon differ from an uninjured pigeon? 

 What is the main function of the cerebellum? What is implied 

 iu each step that we take? 



