228 THE GROWTH OF THE BRAIN. 



tions. Objectively, one measure of central complexity 

 is the modification of the outgoing impulse in response 

 to slight variations in the stimuli. Therefore we should 

 expect that a nervous system composed of a large 

 number of structural elements, well organised, would give 

 more highly modified reactions than one which contained 

 a smaller number though similarly organised. 



To make plain this view, it must be understood that 

 not only are stimuli received through the sense organ 

 which initiates a reaction, but we are all the time 

 receiving concomitant stimuli through the other organs 

 of sense, and as each group of responsive cells or those 

 initiating the outgoing impulses can be influenced in 

 some degree by any of the incoming impulses, it is 

 evident at a glance that an almost endless series of com- 

 binations is possible. For example, a sharp cry may 

 instinctively lead us to draw back from its source. If, 

 however, the visual impression that accompanies the cry 

 arouses sympathy, we draw towards it. The motor 

 reaction in the two cases are opposites to one another, 

 and they are modified by a secondary visual impression 

 accompanying the auditory one. This is a very simple 

 case, but it is an easy matter to imagine the various 

 complications, when it is also remembered that any 

 other sense impression, present or past, may enter in as 

 a modifying circumstance. To regard, therefore, the 

 nervous system simply as a mechanism capable of giving 

 very complex reactions in response to stimuli, implies 

 no more than the acceptance of the every-day point of 

 view, taken when we venture to predict the actions of 

 our neighbour under an anticipated set of conditions. 

 It appears that the more complicated the nervous 

 system of an animal is, the greater is the possibility of 

 those refined adjustments in which several of the sensory 

 elements shall play their proper parts, and each element 



