CUTANEOUS SENSATIONS 101 



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

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

 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 de- 

 scribed form collectively v. Frey's 

 jesthesiometer. In place of these, 

 an instrument is sometimes used F IG . so. v. FRET'S HAIR JSSTHESIOMETER. 

 consisting of a fine blunt needle 



set in a handle, within which is a delicate spiral spring furnished 

 with an index to show the amount of pressure required before a 

 sensation is caused. But in general this is found more difficult to 

 apply than the bristles. 



Graham Brown's aesthesiometer consists of a convex piece of 

 steel with a polished surface, a part of which can be made to 

 project beyond the rest by turning a truly cut micrometer screw. 

 The surface is passed lightly over the surface of skin to be tested, or 

 vice versa. The relative delicacy of touch is gauged by the power 

 of feeling different degrees of projection. 



Discrimination of two points. For this purpose a pair of compasses 

 with blunt points is used ; their distance apart is measured upon 

 a scale after each observation. Or the points may be permanently 

 connected with the scale, one being fixed at its zero and the other 

 sliding along it (Sieveking's sesthesiometer). Test in this manner in 

 another person various parts of the integument (back and front of arm, 

 fingers, lips, tip of tongue, etc.) and record the distances at which the 

 two points are discriminated as separate, causing them always to 

 touch simultaneously, and without lateral movement. 



Accuracy of localisation. This is investigated by lightly touching 

 any part of the skin and immediately causing the subject to place 

 his finger upon the part touched. 



In all the above experiments the subject should be blindfolded. 



