550 KARL T. WATJGH 



indebted to Professor R. M. Yerkes, under whose immediate super- 

 vision the work was carried on, for the suggestion of the problem 

 and for much helpful criticism and advice throughout the course 

 of the work. I wish also to make acknowledgment to Professor 

 Miinsterberg and Professor Holt for their advice and suggestions. 

 The anatomical portion of the work was done in the Museum of 

 Comparative Zoology at Harvard under the direction of Profes- 

 sor G. H. Parker, to whom I am indebted for aid and advice. 



The general method pursued was that of presenting to the 

 mouse a choice between two conditions, one being agreeable to the 

 animal and the other disagreeable. In the majority of cases these 

 were food and a slight electric shock. 



PROBLEM 1. DISCRIMINATION OF LIGHT INTENSITY 



A. Under indirect illumination 



In experiments (a) and (b) under this head, five animals were 

 used. 



DURA1ION OV EXPERIMENT 



No. 1 gray 



No. 2 black 



No. 4 black 



D white 1 



O brown 



1 All the white mice are albinos. 



Apparatus: This consisted of a wooden box measuring 52 

 cm. x 40 cm. on the inside, and 18 cm. deep. At one end of the 

 box was a small opening fitted with a sliding door, which, when 

 lifted, permitted the mouse to enter from the nest box A* (fig. 1). 

 At the other end of the experiment box were arranged two round 

 tin boxes X and Y, each measuring 4| cm. in diameter, covered 

 with papers which differed in brightness, in color, or in both. The 

 boxes were fitted into small wooden mounts fastened to two boards 

 (22| cm. x 18^ cm.). On these boards wires were placed, as is 

 shown in fig. 1. These wires were then connected with a Porter 

 inductorium. By closing the key, K, the experimenter could give 

 a mouse whose feet rested upon two adjacent wares a slight shock. 



