LABORATORY MANUAL OF PHYSIOLOGY. 



ing a hair at right angles to the end of a wooden handle by means 

 of a bit of sealing-wax. If this hair is pressed, perpendicularly, 

 against the skin, it will exert a certain pressure, depending upon 

 the thickness and character of the hair. This pressure can be 

 determined, for any hair, by pressing it against one scale pan of 

 a balance and finding the largest weight that can be lifted in this 

 way. 



(a) Prepare a number of hair aesthesiometers, using hairs of 

 different lengths and thicknesses and estimating their pressure 

 values. 



(b) Gently touch the end of a hair on the back of the hand. 

 Note the sensitiveness of the hair as a touch organ. The end 

 organs of touch are arranged in radiating lines about the roots of 

 the hairs. The hairs act as levers, the long arm projecting above 

 the skin surface and the short arm making pressure against the 

 nerve endings. In this connection consider the so-called touch 

 hairs of the cat and other animals. 



(c) Shave the skin of the back of the hand, and, starting at the 

 hair follicle, map out the touch-spots in an area of 2 sq. cm. Start 

 with a test hair of least pressure and increase the pressure until 

 sensation is produced. The subject of the experiment should be 

 blindfolded and instructed to say yes immediately upon feeling the 

 application of the test object. 



Record the threshold value of the stimulus needed to produce 

 sensation in this region. Record, also, the number of touch-spots 

 present in the area of skin tested. 



What is the arrangement of the touch-spots in relation to the 

 hair follicle? 



(d) Shave the skin of the back of the leg and map out the touch- 

 spots and determine the threshold value of the stimulus, in the 

 same way as was done for the skin of the back of the hand. 



(e) Repeat the experiment for the skin of the abdomen, near 

 the median line and some distance from the median line. 



(/) Test the touch sensation of the skin of the back, over the 

 shoulder. 



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