Modification by Experience 285 



duced by the presence of food in the stomach at a certain 

 time. They have apparently become a part of a system 

 of internal, organic movements, so that when these internal 

 processes have continued for a length of time equal to that 

 which usually elapses between meals, they produce the 

 stomach contractions, in the absence of the original stimulus, 

 the food. Thus the case seems to be like that of the run- 

 ning of the maze by a thoroughly practised animal ; each 

 act is the stimulus for the next, and outside stimuli are 

 unnecessary. 



