FUNCTION OF VIBRISSAE IN BEHAVIOR OF WHITE RAT 47 



every sense and rendered increasingly hard by every defective 

 sense. 



In the rat, for instance, vision is poor and probably only 

 serves to give it general orientation. Hearing, judging from 

 observation is keen and has in it elements of both distance and 

 direction. 25 Olfaction also has in it for animals in which the 

 sense is keen that which may give both distance and direction 

 and, in case of trails, marvelously supplement a defective vision 

 in exact orientation. 



The rat has another compensatory arrangement as this work 

 has tried to show. It has about the mouth an exceedingly 

 sensitive system of hairs. 



Of these vibrissae those curved hairs nearest the nares drag 

 along the surface of the ground and floor and in incessant vibra- 

 tion give immediate stereognostic sensations of contact and 

 support. Projecting slightly in front of the body the failure of 

 this sensory report seems to warn the animal of a ^•oid. The 

 longer hairs arising from the side of the lip may be turned down 

 against the edge of a surface so that the rat may follow it, an 

 act for which poor vision would be ineffective, or these same 

 hairs may graze the side of a vertical surface and furnish evi- 

 dence of protection and guidance as an animal runs. In other 

 words the vibrissae serve these creatures much as a blind man's 

 hands or cane serve him in difficult or unfavorable situations. 

 A rat does not instinctively run along vertical walls and avoid 

 open spaces from fear but instinctively takes the course for 

 which it is best fitted by nature. 



J. Appendix 



Section of nerve. In order to satisfy outselves as to the exact 

 sensory nerve supply to the follicle it was resolved to cut the 

 branch of the trigeminus which innervates it. There was a 

 further reason in that it was desired to use, in the animal ex- 

 perimentation, rats whose noses and vibrissae were entirely 

 insensitive. 



In order that the motor nerve might not be cut the section 

 had to be made before the anastomosis with the facial. This 

 was done with strict antiseptic precautions. The wounds healed 

 readily and in two weeks the animals to be used in the experi- 



25 Note: — A blind rat can be called around a simple maze almost without error. 



