32 



HARRY MILES JOHNSON 



making up an order of presentation at random may too easily 

 fall into a rhythm of his own. 



3. Duration of the stimulus. This should be made as nearly the 

 same for both stimuli as possible. If the animal reacts quickly 

 the stimulus tone may be sounded until choice has been made ; if 

 he reacts slowly, however, the chances are that he will disre- 

 gard the stimulus if its duration is much more than one or two 

 seconds. This may work injury if the animal habitually "sets 

 himself" to react when the stimulus has ceased — as some ani- 

 mals will do. If two tones widely different in pitch are used, 

 the tendency of the higher one to die away more quickly than 

 the deeper, may be a disturbing element; if the animal reacts 

 slowly, both tones should be damped at the end of the time 

 allowed, regardless of the animal's behavior. 



FiGURK 1 — A, home-box; B, iniroductory alley; C, opening; into alleys D and 

 D'; E, E', alleys entering food-comjiartments F and F'; G, G', punishment 

 grills; T, table containing stimulus-forks. V, W, X, X', Y and Y' are doors, 

 automatically swinging in the direction indicated. The experimenter's place 

 is in an adjacent room by window O in front of door V of the home-box. 



