TACTILE HAIR OF THE WHITE RAT 23 



about the neck of the folhcle will dampen the vibrations. These 

 are probably under efficient reflex control. 



Several reflex phenomena are the result of the nature of this 

 stimulus and the mode of its application. Only vibratory or 

 intermittent stimuli are the adequate stimuli for certain reflexes. 

 According to Sherrington ('06) a scratch reflex which cannot 

 be evoked by a single induction shock, or even two unless very 

 intense, can be produced by a series of subliminal stimuli (44 in 

 one instance) through spinal power of summation. The same 

 reflex may be produced by a rub, prick or pull upon a hair; but 

 as he says, "there is nothing to show that these stimuli, though 

 brief, are really simple and not essentially multiple." 



The following statement is taken from von Frey ('96, p. 238) : 

 ''The significance of the hair is less in the perception of passive 

 weight than in the perception of fleeting impressions, or moving 



stimuli The hair functions as a lever. The nerve 



excitation is not the effect of pressure but the expression of a 

 vibratory movement." Perhaps such vibratory stimuli are ade- 

 quate because they lead to summation. 



A vibratory stimulus besides its summating power has, in the 

 nature of things, a tendency to prolong the initial stimulus. 



Another condition which increases the tactual power of these 

 organs is the muscular connection of one follicle with another, 

 so that there is a general spread of excitation, irradiation of 

 stimulation over a comparatively wide area. 



The erectile tissue and blood sinuses are in a sense necessary 

 to the free vibration of the hair and stimulation of the end organs. 

 This free vibration could not occur if the hair shaft were fixed in 

 a firm unyielding tissue. They may also, as others have pointed 

 out, serve to increase or modify the pressure, but as the pressure 

 is not directly exerted through the skin the modification must be 

 brought about through the varying resistance offered to the 

 excursions of the hair shaft itself. The erection of this vascular 

 tissue may also, as Dr. Herrick has suggested, lower the nervous 

 threshold as compared with that of the flaccid state and an effi- 

 cient reflex control be brought about in this way. Those who 

 believe that all sensation is chemical in origin may see in this 



