60 G. V. HAMILTON 



mere inattention or forgetfulness have interfered with an ade- 

 quate expression of the rational inference tendency. 



Type C. This highly interesting mode of adjustment can 

 occur, as has been explained, only when Door i or Door 4 is the 

 unlocked door for the trial. It involves merely the act of trying 

 (i) Doors I, 2, 3 and 4 but once each and in the order given 

 when Door 4 is the unlocked door, or (2) doors 4, 3, 

 2 and I but once each and in the order given when 

 door I is the unlocked door. The habit of starting at 

 either the first or the last door from the left and working down 

 the line of doors, striking each as it is passed until an unlocked 

 door is found, deserves, in itself, a far more extensive investiga- 

 tion than it has thus far received. My observations of the 

 higher infra-human mammals, of children and of mentally 

 defective or diseased persons lead me to believe that in this 

 mode of adjustment we have the expression of a reactive ten- 

 dency which has extensive genetic relationships, and which 

 can be more easily recognized in behavior than can any other 

 reactive tendency of which we have knowledge. In the discus- 

 sions that follow Type C reactions will be referred to as due to 

 ' ' the tendency to adopt stereotyped modes of searching. ' ' 



Type D. This reaction involves the error of making more 

 than one separate, continuous effort to open a given door during 

 the same trial, but always with an interruption of such repeti- 

 tions of activity by an interval of effort to open one or more 

 of the other doors. Since this mode of adjustment is objectively 

 continuous with a form of Type E reaction (sub-type c, described 

 below), and yet clearl)^ should not be made to include the latter, 

 I have excluded from Type D all reactions involving more than 

 six separate efforts to open doors during a given trial. 



A characteristic example of the Type D reaction will render 

 its interpretation more intelligible. During his fortieth trial 

 Dog 16F2 made a vigorous effort to open Door i, which was 

 locked; failing in this effort, he tried to open Door 2, which 

 also baffled him in his efforts to escape. Then he returned to 

 Door I and made a second effort to open it by giving it two or 

 three feeble scratches, after which he tried Doors 3 and 4, the 

 latter of w^hich yielded to his attack. 



Anybody who has ever sought vainly, and with some irrita- 

 tion, a lost collar button, will readily appreciate the inner sig- 



