422 FEELING AND TOUCHING. 



Estimate of ^ toucn ' We should make a distinction, however, with 

 physical quail- Magendie, between feeling and touching, the former being 

 essentially passive, the latter active; and though we usu- 



su PP ose that, ^ a ^ our senses, touch is the most reli- 

 and touching, able, it often conveys to the mind illusory impressions, as, 

 for instance, in the well-known experiment of Aristotle, when the tips of. 

 the fingers are crossed over each other, and a pea rolled beneath them, it 

 seems as if there were two peas, one under each finger. The indications 

 of touch are generally more correct than those of feeling. Thus, if we 

 close our eyes, and another person moves the tip of our finger over an 

 unknown surface, he can completely deceive us by duly varying the press- 

 ure, and make us believe that it is concave or convex, whereas it may be 

 flat ; but if we pass our fingers over the surface ourselves, we very quick- 

 ly come to a true conclusion, because now we are conscious of the exer- 

 tion of muscular power ; and from what has been said respecting hearing, 

 we may infer how delicate our estimate of muscular exertion is. The 

 former is therefore an example of feeling, the latter .of touch. 



Connected with this distinction are the singular phenomena of tick- 

 ling ; the regions most readily affected by this are those of low 

 tactile sensibility. A person can not tickle himself, though it 

 is said that cases are upon record in which one has been tickled to death 

 by another. As in the other cases, the mind can direct attention exclu- 

 sively, for the time being, to some one indication of touch, which, though 

 it may be apparently insignificant in itself, becomes, after a while, per- 

 fectly intolerable, as the pressure of a hair, a gentle draught, or the fall- 

 Remains of im- m g f water, drop by drop, on the top of the head ; and, as 

 pressious. w ith them, an impression which is made does not instanta- 

 neously disappear, but will sometimes continue for quite a considerable 

 time. A ring or other article that has been long worn will leave a sen- 

 sation, though it may have been removed. 



Besides affording an estimate of external pressures, the sensory organ 

 enables us to discover variations of temperature. It may therefore be 

 thus effected by bodies upon contact or by bodies at a distance ; and 

 Perception of though we usually confound the two indications together, 

 temperature there is, in reality, a distinction between them ; thus, in cer- 



distmctfrom . . J ,.,.,.. _ , 



that of press- tain conditions of paralysis, the indications of the contact of 

 bodies may remain, but those of heat and cold may have to- 

 tally disappeared. On examining a surface from which the skin has 

 been removed, it does not appear capable of distinguishing hot from cold 

 bodies, but only communicates to the mind an indefinite sensation of 

 Ideas of heat pain ; nor can we create sensations of heat or cold by any ir- 

 nof arise Trd- ritati( > n ^ the nerves. The measure of temperature by the 

 ficiaiiy. agency of the skin is very far from being exact, as has been 



