FUNCTION OF VIBRISSAE IN BEHAVIOR OF WHITE RAT 53 



PART II. TACTUAL DISCRIMINATION 



DIVISION I. EXPERIMENTATION, 



to determine whether the vibrissae of the white rat aid in the discrimination of 



roughness of surface 



While the work of the animals on the maze showed conclu- 

 sively the effectiveness of the vibrissae in such representative 

 situations, there was still left the open problem as to whether 

 these organs could function in other tactual ways, whether they 

 could mediate sensations of roughness or discriminate inequal- 

 ities of surface. That they had a part in the regulation of equi- 

 librium we know; that they contributed "guiding sensations" 

 in the control of locomotion ; that they were closely linked up 

 with the kinaesthetic system in determining sequences of turns, 

 "rightness" and "leftness;" but could they or did they, in the 

 animal's experience, serve as agents for those other tactual 

 qualities, contact values, of surface. 



The experimentation which is reported in Part II was under- 

 taken to determine this point. In the course of it, however, 

 the general problem of discrimination arose in such a character- 

 istic way that there has been added a brief discussion of some 

 of the features of the act as a whole, in the light of the specific 

 behavior observed in this problem. 



A. Description of Apparatus 



The box used in this experiment (see fig. 12 p. 54 and fig. 19. 

 Plate IV), was made of three-quarter inch stuff and its dimensions 

 were 5 ft. x 2 k ft. Two cross pieces were set one foot from 

 either end, dividing its length into three parts, the entrance, 

 the runways, and the food box. The runways, each four inches 

 in width, were formed by six partitions set lengthwise in the 

 middle of the box. These dividing walls measured 3 ft. x 5 in. 

 and one side of each was lined with zinc. Two had corrugated 

 and four had plain linings and the partitions were set in grooves 

 so that they could be lifted and interchanged and thus the 

 corrugated i-unway could be in any one of the three positions. 

 The whole box, including the walls and linings was painted 

 black. From the entrance there were free openings into the 

 alleys A, B, and C, but at the end of these alleys in the cross 

 piece doors were hung from above which could easily be pushed 



