SENSATION. 



(g) Map out the touch-spots of the cheek, starting near the lobe 

 of the ear and proceeding to the angle of the mouth. In what part 

 of this area are the touch-spots most numerous ? 



(k) Test the mucous membrane of the upper and lower lips in 

 the same way. 



(i) Test the palmar surfaces of the finger tips; of the hand. 



How do the threshold values of the efficient stimuli, for the 

 various regions tested, compare? Is there any relation between 

 the number of touch-spots and the mobility of the regions tested ? 



(j) Repeat experiments (a) to (i), using, instead of the test 

 hairs, a series of weights of the same surface area (about 4 sq. mm.) . 

 Begin with a weight of 0.0005 gm. and increase until the sensation 

 is obtained. How do the threshold values compare with those ob- 

 tained with the test hair ? In the first series of experiments, single 

 touch-spots were stimulated. In the second series, a number of 

 touch-spots were stimulated simultaneously, the number varying 

 with the region of skin to which the stimulus was applied. 



The efficacy of any particular stimulus will depend, to a large 

 extent, upon the number of touch-spots in the area stimulated, 

 the proximity of the end organs to the skin surface, and the deforma- 

 tion of the skin effected by the stimulus. The temperature of the 

 weights employed should be approximately that of the skin. 



(k) Take a number of pieces of flat cork, cut into strips about 

 3 cm. long, i cm. wide, and i cm. thick, and pass blunted needles 

 through the ends of the strips so that the distance between the 

 needle-points of the different pairs varies from i to 25 mm. 



With a blindfolded subject, test the ability of the skin of various 

 regions to detect the application of the different pairs of needles as 

 two separate stimuli. The subject should answer, immediately 

 upon the application of the stimulus, one or two, as the sensation 

 is that of one point or two points. 



In this way test the sensitiveness of the skin of the finger-tips, 

 the back of the hand, the shoulder-blade, the forehead, the cheek, 

 the lips, the tip of the tongue, the skin of the thigh in its long axis, 

 the skin of the thigh in its short axis. 



