MENTAL EVOLUTION OF MAN 209 



promptitude of reactions to stimuli. In certain re- 

 spects intelligence seems to differ from instinct, inas- 

 much as it involves a response to stimuli that may- 

 be altered and quickened by repeated experience, but 

 in ultimate analysis the two forms of psychological 

 processes are fundamentally alike. A single example 

 chosen from Thorndike's extensive investigation will 

 serve to bring out the primary characteristics of intelli- 

 gence. A cat was placed in a latticed cage provided 

 with a door that could be opened from within when a 

 catch was pressed down, and meat was put in a dish 

 outside the door where the cat could see it. At first, 

 the animal escaped from the cage by freeing the door 

 during its aimless scrambling about the catch, but as 

 trial after trial was made, the time necessary for the 

 cat to make its way out was shortened, until after 

 seventy-five or one hundred trials, the animal imme- 

 diately opened the door and seized the food. In me- 

 chanical terms, the connection between " scrambling 

 about the door " and " freedom to get the meat " be- 

 came established by numerous repetitions until the 

 originally disconnected elements were physiologically 

 associated and made inseparable. Wlien animals like 

 horses and seals and dogs are trained for the circus, it is 

 by exactly the same method, for training consists merely 

 in the establishment of a psychological sequence so that 

 the performance of one series of acts leads mechanically 

 to others. Thus we learn that the psychological prop- 

 erty called intelligence is the ability to establish wide 

 relations between numerous activities which are them- 

 selves of a more or less complex nature ; and we find 

 also that because these elements are ultimately nerve- 



