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MILDRED A. HOGE AND RUTH J. STOCKING 



Figure 1. Discrimination box (after Professor Yerkes). A, nest- box; I, door 

 leading into entrance chamber B. The floor of the compartments W and W 

 are wired to give electric shock. P, partition between the two compartments; 

 V, V, doors leading into alleys which have doors O and O' leading back into 

 compartment. A, C and C' are the light chambers, never entered by the rats. 

 These are separated by the partition P'. The two chambers are light-tight 

 and were kept tightly covered during test. S and S' are the standard stimulus 

 plates. 



