Habit Formation : Discrimination Method 229 



box without shock or hindrance, the training was begun. 

 These two preliminary series serve to indicate the natural 

 preference of the animal for white or black previous to the 

 training. An individual which very strongly preferred the 

 white might enter, from the first, the box thus distinguished, 

 whereas another individual whose preference was for the 

 black might persistently enter the black box in spite of the 

 disagreeable shocks. First of all, therefore, the preliminary 

 tests furnish a basis for the evaluation of the results of the 

 subsequent training tests. On the day succeeding the last 

 series of preliminary tests, and daily thereafter until the ani- 

 mal had acquired a perfect habit of choosing the white box, 

 a series of training tests was given. These experiments 

 were usually made in the morning between nine and twelve 

 o'clock, in a room with south-east windows. The entrances 

 to the electric-boxes faced the windows, consequently the 

 mouse did not have to look toward the light when it was 

 trying to discriminate white from black. All the conditions 

 of the experiment, including the strength of the current for 

 the shock, were kept as constant as possible. 



Choice by position was effectively prevented, as a rule, 

 by shifting the cardboards so that now the left now the right 

 box was white. The order of these shifts for the white- 

 black series whose results are quantitatively valuable appear 

 in Table 12 (p. in). That the order of these changes in 

 position may be criticised in the light of the results which 

 the tests gave, I propose to show hereafter in connection with 

 certain other facts. The significant point is that the defects 

 which are indicated by the averages of thousands of tests 

 could not have been predicted with certainty even by the 

 most experienced investigator in this field. 



In Table 41 are to be found the average number of errors 

 in each series of ten white-black discrimination tests for five 



