8 

 maze or hood Of the latch-box or inclined plane box. It 



was taken the entire period the rats remained in the hood 

 or maze and up to the moment the problem was solved; that 

 is, when the rats entered the center of the maze, or when 

 the latch of the latch-box was raised, or when the plane 

 of the inclined plane box was pushed down. 



The next thing to consider is the incentive to activi- 

 ty. In all experimentation, food was used as a stimulus 

 and consisted of a preparation of bread and milk. Be- 

 sides this mixture grain and, occasionally, fruits were 

 added. When food is properly controlled it becomes one 

 of the best stimuli to arouse activities. Behavior under 

 the desire for food or stimulation of hunger is in the 

 nature of a normal life process. A mild degree of hunger 

 gives tonicity to the muscles, and movements are sudden, 

 numerous and active. In order to obtain the greatest 

 activity, and not disturb general metabolism, particular 

 attention "must be paid to the kind as well as the amount 



