312 ON SENSATION AND THE UNITY OF 



fied by the development of hair-like filaments, or 

 of true hairs, the bases of which are in immediate 

 relation with the ends of the sensory nerves. 

 Every one must have noticed the extreme delicacy 

 of the sensations produced by the contact of 

 bodies with the ends of the hairs of the head; and 

 the "whiskers" of cats owe their functional im- 

 portance to the abundant supply of nerves to the 

 follicles in which their bases are lodged. What 

 part, if any, the so-called "tactile corpuscles," 

 " end bulbs," and " Pacinian bodies," play in the 

 mechanism of touch is unknown. If they are 

 sense organs, they are exceptional in character, 

 in so far as they do not appear to be modifica- 

 tions of the epidermis. Nothing is known respect- 

 ing the organs of those sensations of resistance 

 which are grouped under the head of the mus- 

 cular sense; nor of the sensations of warmth and 

 cold; nor of that very singular sensation which we 

 call tickling. 



In the case of heat and cold, the organism not 

 only becomes affected by external bodies, far 

 more remote than those which affect the sense of 

 smell; but the Democritic hypothesis is obviously 

 no longer permissible. When the direct rays of 

 the sun fall upon the skin, the sensation of heat is 

 certainly not caused by "attenuated films" thrown 

 off from that luminary, but is due to a mode of 

 motion which is transmitted to us. In Aristote- 



