280 THE HUMAN MECHANISM 



cooperate to make thought visible; performing on a musical 

 instrument, modeling a figure in clay or marble or bronze, 

 painting a picture all these things occur to us as examples 

 of movements which are fundamentally neither reflex nor 

 automatic. Such are the highest actions of the body, and 

 the movements of which these actions are made up are 

 chosen and directed by the will. 



These higher actions, like consciousness, depend upon the 

 presence of the forebrain. When a certain area of the cere- 

 brum is destroyed by disease, the power of speech is lost; 

 when another part is destroyed, the skilled use of the hand 

 is lost ; destruction of other portions affects in the same way 

 others of these skilled movements. In such cases locomotion, 

 the maintenance of balance, the movements of respiration, 

 etc. may be and usually are unaffected; the patient merely 

 loses the power of doing one or more of those things which 

 involve the selection of disconnected and to some extent 

 independent movements giving expression to some original 

 thought, sentiment, or idea. 



The neurones of the cerebrum and their connections thus 

 constitute nervous mechanisms whose activity is essential to 

 consciousness, to our seeing, our hearing, our smelling, and, 

 more than this, to our understanding of what we see, or hear, 

 or smell, nervous mechanisms whose activity is also neces- 

 sary to the expression of our thought in action. It is because 

 of this fact that, when the cerebrum is removed, the animal 

 becomes merely a complicated reflex machine, acting only 

 as it is immediately stimulated from without or by events 

 taking place within its own body. 



14. Effects of anesthetics on the nervous system. When 

 a person passes under the influence of an anesthetic, the 

 first function to disappear is consciousness; the ether or the 

 chloroform first paralyzes this highest and most complex 

 connection between the afferent and the efferent sides of 

 the nervous system. In this condition the patient may groan 



