292 STUDIES IN PHYSIOLOGY 



Sensations of Touch. If I rub a piece of cloth over the 

 tip of my finger, I can determine, even with my eyes closed, 

 whether the cloth is smooth or rough. Its characteristics 

 could be determined even more accurately by rubbing it 

 on the lips or forehead. But if I were to apply the piece 

 to the back of my neck, I should find the latter to be far 

 less sensitive than are the lips and finger tips. The degree 

 of sensitiveness of the various parts of the body can be 

 determined very accurately in the following way. When I 

 separate the points of a pair of scissors about three inches, 

 and, with my eyes closed, apply the two points to the back 

 of my neck, I can get a distinct impression of each. When, 

 however, the points are brought within two inches of each 

 other, they give the sensation of a single point. If the 

 points are applied to the lips, they can be distinguished as 

 two, even when within about one sixth inch, and on the tip 

 of the tongue the points need be separated but one twenty- 

 fourth of an inch. 



It is interesting in this connection to note that the degree 

 of sensitiveness of a given part can be increased by train- 

 ing. For instance, one experimenter found that on a certain 

 portion of his arm, at the end of a week of training, he 

 could distinguish the points as two when they were sepa- 

 rated about three quarters of an inch; at the end of the 

 fourth week of training, they could be felt as two even when 

 only one sixth of an inch apart. In other words, he had 

 by training his brain increased the sensitiveness of the area 

 experimented upon more than four times. 



The following simple experiment shows how easy it is for 

 one to be mistaken in regard to the judgment of one's sense 

 impressions. If I close my eyes, cross my middle and fore- 

 finger, and then place between the two finger tips a small 

 marble or pea, I seem to be touching two distinct objects. 

 This is due to the fact that under ordinary conditions it is 

 impossible to touch an object at the same time with the 

 thumb side of the forefinger and with the little finger side 



