SENSATION AND THE SENSIFEROUS ORGANS. 273 



extreme delicacy of the sensations produced by the con- 

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

 and the " whiskers " of cats owe their functional impor- 

 tance 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 " Pacini- 

 an bodies," play in the mechanism of touch is unknown. 

 If they are sense organs, they are exceptional in charac- 

 ter, in so far as they do not appear to be modifications 

 of the epidermis. Nothing is known respecting the or- 

 gans of those sensations of resistance which are grouped 

 under the head of the muscular sense ; nor of the sen- 

 sations 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 permissi- 

 ble. 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 Aristotelian phrase, it is the form without the mat- 

 ter 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 any- 

 thing but the impulses or vibrations originated by ^sonor- 



