388 JOHN LINCK ULRICH 



tion of the movements of rats before being admitted to the 



hood. 



The underside of the latch was 2.5 cm. from the top of the table 

 on which the problem box rested. This measurement was equal 

 to the average height of rats 50 days old. This height was de- 

 termined by experimentation, and was considered the most sat- 



FIG. 1. LATCH-BOX PROBLEM 



isfactory, in order to produce the most effective upward head- 

 neck movement. When the latch was placed lower, the rat 

 was found to assume an excessively crouching position; and when 

 it was placed higher than 2.5 cm. the head-neck movement was 

 often completed before the latch was raised out of the notch. 

 The mechanism of the problem was thus adjusted to that of the 

 reflex movement of the head. 



