TACTILE HAIR OF THE WHITE RAT 21 



the use of these tactile organs. The vibrissae were turned down 

 and trailed along the edges of narrow supports or they brushed 

 the sides of vertical walls or the path beneath as the animal ran. 

 Animals deprived of them learned such problems less easily and 

 had many more slips and falls. The inference was drawn that 

 they furnished guiding sensations, sense of support, in locomotion, 

 that they were intimately connected with equilibration and that 

 their extreme mobility and sensitivity in rats was a partial com- 

 pensation for poor vision. This was confirmed in part by obser- 

 vations of rats whose labyrinths had been destroyed. The tactile 

 hairs seemed also to assist in determining the exact position of 

 openings or turns and in the discrimination of inequalities of 

 surface. Animals in which the sensory nerve to this region had 

 been cut, and whose noses as well as vibrissae were insensitive, 

 were unable to make this tactual discrimination. A careful rec- 

 ord of the return of sensitivity to the vibrissae of these operated 

 animals was kept for seven months. One of the most conspicu- 

 ous features of this period was the trophic changes in the hairs. - 

 They curled, split, grew brittle, and finally broke off and at the 

 end of seven months when the nerves were regenerating and 

 sensibility was returning many animals had not half as many of 

 these hairs, and of those present many were broken and imper- 

 fect. The wound healed without suppuration. In two weeks the 

 animals were in perfect health. The sensory innervation of the 

 follicle appears in some way to be the stimulus to, or condition for 

 the growth and maintenance of the hairs by whose movements 

 the nerve endings themselves are excited. 



The complete details of the experimentation, the mode of opera- 

 tion and the tests for sensitivity are described in my monograph. 

 The Function of the Vibrissae in the Behavior of the White Rat 

 (Vincent '12). 



The attempt to explain structure by physiological function has 

 not been on the whole successful. Messenger ('05) bases his 

 account of the haemostatic structure of the follicle on the absence 

 of erector muscles; but there are muscles in sufficient number 

 to account for all the movements of the hairs. 



