26 ROBERT M. YERKES 



in use. The special equipment consists of a concealed incan- 

 descent electric lamp for the illumination of each box and an 

 electric signal and timing mechanism for the operation of the lamps 

 and the door between the release box and the reaction chamber. 



The method of delayed reaction may be used with various 

 groups of doors, according to the grade of difficultness of re- 

 sponse desired. Thus, as the simplest situation, boxes 6 and 

 8 may be used. In this case, the entrance doors of both boxes 

 should be raised in preparation for a trial. The doors of the 

 other boxes should remain closed. In accordance with a pre- 

 arranged plan, either the one or the other box would be indi- 

 cated, by momentary illumination, as the box to be chosen. 



For the second grade of difficultness, boxes 5, 6, 7 and 8 might 

 be used, each of them having the necessary equipment and con- 

 nections for use as the correct box; for grade three, boxes 2, 5, 

 8 and 11 ; for grade four, boxes 1, 3, 5, 7, 9 and 11 ; and for grade 

 five, all of the twelve boxes might be subject to use, that is, the 

 entrance door of every box should be open and the subject should 

 be required to choose that one of the twelve which has previously 

 been illuminated. 



The satisfactory use of this method necessitates not only the 

 presence of a lamp, but the installation of a mechanism which 

 shall control several important factors in the situation. The 

 experimenter, by pressing a simple key, should close a circuit 

 which at once illuminates a certain box (the particular box to 

 be determined by the setting of a switch), and at the same time 

 starts a timing mechanism. This mechanism should, after an 

 interval, with a range of 1 to 10 seconds, open the lighting cir- 

 cuit, thus cutting off the illumination of the correct box; and 

 after an interval of to 60 seconds it should cause the door 

 of the release box to open so that the animal may enter the 

 reaction chamber. For intervals longer than 60 seconds, it seems 

 best to have the experimenter determine the delay by means of 

 a stop watch and operate the door of the release box by hand. 



There is no obvious reason why this twelve mechanism reac- 

 tive tendency apparatus should not be used in wholly satisfac- 

 tory fashion for the study of delayed reactions. The additional 

 electrical equipment should in no wise interfere with the other 

 uses of the apparatus and that portion of it which controls the 

 release box door might be made to serve the experimenter in 

 connection with all of the methods. 



