FUNCTION OF VIBRISSAE IN BEHAVIOR OF WHITE RAT 69 



tical although the animals were used in three groups by two 

 experimentors, and one group was separated from the others 

 by an interval of eight months.^" 



Summary 



This part of the experimentation was undertaken to discover 

 whether the tactile hairs had any part in the discrimination of 

 surfaces. The results show that they do. Not only is the number 

 of trials in learning greatly increased by their removal but the 

 time per trial is greatly lengthened. The work also seemed to 

 show that the power of discrimination which remained after the 

 removal of the vibrissae lay in the very sensitive nose since the 

 blind rats and the anosmic rats could make the discrimination 

 while rats with insensitive noses as well as vibrissae failed. 

 The experimental work seemed to show as well that in such a 

 problem as this the chief use of olfaction and vision is in initiat- 

 ing action and by a tonic effect sustaining it. These hairs then 

 as the w^hole work shows are delicate tactile organs, which 

 function in equilibrium, locomotion, and the discrimination of 

 surfaces in distinct ways which have been described and the 

 inference is drawn that the great innervation and fine mobility 

 to which the increased sensitivity of these organs in rodents is 

 due has arisen in compensation for an exceedingly poor vision. 



DIVISION II. GENERAL DISCUSSION 

 There are always points of interest in any experiment which 

 do not directly concern the main problem. A few of these in 

 connection with this work have already been mentioned but 

 some of the more general phases of the act of discrimination 

 seem worth while considering now. The discussion is related 

 to the discriminative process in general but is based upon the 

 observations and experimental results which have been reported. 



30 aJote: — There were two normal animals belonging to group three whose records 

 are not included in the averages. One rat, a female, had some trouble, perhaps 

 in the vestibular tract, which pulled her over to one side, made her revolve in circles 

 and rendered locomotion difficult. This came upon her soon after the experi- 

 mentation began but her work was continued and she learnetl the problem at the 

 278th trial. It seemed unfair to class this animal with tlie normal ones. The 

 other rat was the one spoken of before that never succeeded in learning the problem 

 although given 4(30 trials covering a period of 95 days. 



Miss Mothershead ran one of these groups of normal rats and I am greatly indebted 

 to her for her records and observations. 



