CHAPTER XXVIII 

 Cutaneous Sensations 



Cutaneous sensations. Pain spots. Explore with an ordinary pin 

 or needle a portion of the skin of the forearm or back of the hand 

 of another person (who should keep his eyes closed, or look the other 

 way), pressing the point firmly here and there, but without penetrating 

 the surface. Notice that whereas at some places the prick is painful, 

 at others no pain is caused, the feeling being either one of touch or 

 pressure (or no sensation is produced). 



Warmth spots. Substitute for the pin a thick copper rod with a 

 smooth point ; the rod may be provided with a wooden handle. Warm 

 the rod by immersing it in water heated to 45 O. Explore the skin by 

 passing the warm point of the style slowly over it. It will be found 

 that the sensation is one of warmth only at certain points, where it is 

 very distinct ; at others it is merely a sensation of touch. 



Cold spots. Repeat after cooling the rod by immersing it in ice- 

 cold water. In this way spots sensitive to cold alone can be picked 

 out : they are not the same as those which are sensitive to warmth. 



The various spots may be mapped out upon a patch of the skin with 

 coloured inks or pencils, and may be tested again later. They are 

 constant in position. 



Touch sensations : Determination of the relative delicacy of different 

 parts to touch. Take a fine bristle or coarse hair 2 inches long, and 

 fix it with sealing-wax to a match to serve as a holder (Fig. 87). Ex- 

 plore in another person (who is not to see the part which is touched) any 

 part of the skin, determining the spots which are most sensitive to the 

 pressure of the hair. The point of this is to be brought vertically on the 

 skin without lateral movement and pressed down only just enough to 

 bend it slightly. By using a number of bristles of different thickness 

 a certain rough scale of delicacy of touch on different parts of the body 

 can be made out. Notice that the slightest side-movement greatly 

 increases the sensitiveness of any part to the touch, especially if hairs 

 are deflected. This can also be shown with a scrap of cotton-wool, 

 the touch of which may be imperceptible until it is moved. 



The series of bristles just described form collectively v. Frey's 



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