266 SENSATION AND THE SENSIFEROUS ORGANS. [LECT. 



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 

 importance 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 modifications of the epidermis. Nothing 

 is known respecting the organs of those sensations of 

 resistance which are grouped under the head of the 

 muscular 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 trans- 

 mitted to us. In Aristotelian phrase, it is the form 

 without the matter of the sun which stamps the sense 

 organ ; and this, translated into modern language, 

 means nearly the same thing as Hartley's vibrations. 

 Thus we are prepared for what happens in the case of 

 the auditory and the visual senses. For neither the 

 ear, nor the eye, receives anything but the impulses or 



