GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM 141 



A Normal Animal Compared with a " Reflex " One. Let us 



imagine that we have side by side before us two living animals of 

 the same species, one normal in every respect, the other in the 

 "reflex" condition; that is, having had the cerebrum destroyed. 

 Disregarding for the present the phenomenon of consciousness and 

 looking at both animals simply as pieces of machinery three strik- 

 ing differences between them are manifest: 1. The " reflex " animal 

 always responds to adequate stimulation by a predictable response; 

 the intact animal sometimes responds and sometimes does not. 

 2. The " reflex" animal does not move except when stimulated, 

 while the intact animal often moves without any apparent rea- 

 son. 3. The amount of response given by the "reflex" animal 

 bears some relation to the intensity of the exciting stimulus, 

 whereas in the normal animal an apparently feeble stimulus may 

 arouse a vigorous and long-continued response. An example of 

 this last is the running of a dog to its master upon hearing his 

 whistle. The stimulus may be a very faint one, the motions 

 which it arouses are exceedingly vigorous and complicated. 



All these differences depend at bottom upon a single funda- 

 mental difference between the two animals which is this: in the 

 "reflex" animal the immediate stimulus dominates the situation 

 completely; in the intact animal the immediate stimulus is only 

 one factor of many which together determine what the response 

 shall be. The superior practical efficiency of the intact animal 

 as an adaptive organism depends upon this power, resident in the 

 cerebrum, of modifying immediate stimuli in accordance with the 

 demands of less obvious considerations. To illustrate: a hungry 

 man perceiving food would inevitably respond to the double 

 stimulus of hunger and the sight of food by taking the food and 

 eating it if he acted upon a purely reflex basis ; his actual response 

 to these stimuli will depend, however, upon whether they are in 

 harmony with or opposed to certain more remote factors, such as 

 the question whether the food is of a sort that will agree with him, 

 or whether he is likely to need it more urgently at some future 

 time than at present. 



Before entering upon a fuller discussion of the functions of the 

 cerebrum, its structure and its connections with lower nerve-cen- 

 ters must be described. 



