TOUCH ' 101 



tance at which they can be distinguished, say four out 

 of five times, is the threshold. 



If the points are separated a little less than the threshold, they 

 will probably be felt as two if they are more down the arm, or if 

 they are put transversely to the arm. 



When the approximately minimal distance is reached 

 at which A does not distinguish the two points, he is 

 told to open his eyes, and observe the application of the 

 points. 



A shuts his eyes once more, and the points are applied 

 to the tip of the fore-finger ; the points being at first 1 cm. 

 apart, -75, and so on; now T and then a single point being 

 applied. The threshold will probably be less than -5 cm. 

 A opens his eyes, the points are applied at a distance a 

 little above the threshold. 



Similar observations may be made on other parts of 

 the body. 



If the threshold is determined for the back of the neck, the two 

 points being applied on either side of the mid-line, it will probably 

 be found that they are not distinguished if they are applied longi- 

 tudinally, or both on one side of the neck. 



2. Cold spots in the skin. Take two metal rods 1 to 

 1-5 mm. in diameter and rounded at the ends and dip 

 them into a freezing mixture or into ice and water, dry 

 before using (the rod may also be cooled by dipping it 

 into ether, and allowing the ether to evaporate). Mark 

 out with dilute Bismarck brown an area about 2 cm. 

 square on the fore-arm. Lightly press the end of a rod 

 on one corner of the enclosure for 2 sees. ; if it is felt as 

 cold, mark it brown, if not place the rod on the imme- 

 diately adjoining spot of skin, and so along the side of 

 the square, marking all the points felt as cold. Map out 



