U32 ON CUTANEOUS SENSATIONS. [BOOK m. 



is difficult to understand how, if the change be one from a higher 

 to a lower temperature, the lower temperature, whatever may have 

 been the exact degree of the higher temperature, should in giving 

 rise to sensations of cold affect one set of fibres only, or how the 

 higher temperature should similarly affect another set of fibres 

 only ; but we must leave the matter here. 



The considerations which have just been brought forward in 

 relation to sensations of heat and cold, may be also applied to 

 sensations of pressure ; with regard to them also we are driven 

 to the conclusion that they take origin in the lower layer of the 

 epidermis through some condition brought about by the pressure. 

 We can appreciate pressure by the cornea, from which as we have 

 said dermic organs are absent. If the 'points of skin' in various 

 parts of the body, determined experimentally to be points of 

 pressure sensation, be extirpated and examined it is found that 

 dermic organs are not necessarily present ; indeed such points of 

 pressure sensations do not differ essentially in structure from 

 points of heat or cold sensations, though some slight difference in 

 the manner of distribution of the dermic nerve filaments has been 

 described. 



We are thus brought to the conclusion that the so called touch 

 corpuscles are in no way essential to touch. At the same time 

 their remarkable prominence in those parts of the skin in which 

 touch is most sensitive would seem to shew that, even if not 

 necessary, they are in some way adjuvant to pressure sensations. 

 But what that aid may be is at present a mere matter of specula- 

 tion ; and we are perhaps still more in the dark as to the functions 

 of the end-bulbs and of the Pacinian bodies. 



