THE PROPERTIES OF EA< II I'AKT OF THE KEFLEX ARC 



hot bath may really depend on the fact that in the tatter the cold s] 



are stimulated as well as those of heat. It is at least interesting to note 

 thai the physiological reflexes stimulated by either a cold or a very hoi 

 bath are the same; thus, a rise of blood pressure and a contraction of the 



muscles of the skin occur in both eases. 



The Touch Sense. — In order to investigate the tonch sense fcely, 



von Fvcy has devised a method of asing hairs of differenl thickness each 

 mounted on a different handle. The hair which prodn * 1 « » 1 1 



of touch when pressed on the skin so that it just 1m ads is then similarly 

 pressed on one scale pan of a balance, and the weight required in the 

 other scale pan to hold the heam horizontal -when the hair just hends, is 

 ascertained. From the diameter of the hair one can then calculate how 

 many grams per square millimeter are necessary to elicit the Bensation 

 of touch. The following quantitative results have been ohtained by ap- 

 plying von Prey's method to different parts of the body: 



Gm. per sq. mm. 



Tongue and nose 2 



Lip 2.."> 



Finger tip and forehead ?• 



Back of finger 5 



Palm 7 



Forearm 



Back of hand 12 



Calf, shoulder 16 



Abdomen 2fl 



Outside of thigh 



Shin and sole 2*5 



Back of forearm 



L"in )v 



That the sense of touch is located in spots — touch spots — can best 1"' 

 demonstrated on the calf of the leg. Tf this is shaved and then carefully 

 explored with a fairly stiff hair, it will he found that there are only 

 some twelve to fifteen spots in an area of a square centimeter at which 

 the hair can he felt. Between these spots there is no sensation of touch. 

 That these spots are composed of specialized receptors can he very clearly 

 shown by pressing a fine needle into one of them, when no pain will he 

 experienced hut only a peculiar shotty sense of pressure. 



Careful examination of the position of the touch spots will further 

 show that they are grouped around hair follicles, particularly on t : 

 front which the hair extends the windward ride, v 6 may call it. This 

 fact explains 1he well-known experience that an object may he felt n 

 acutely on a hairy surface than after that surface has been shaved. The 



hairs bend slightly when the objeel eomes in contact with them, thus 



