194 EXPERIMENTAL PHYSIOLOGY. 



exception of the temples, the lower eyelids and the cheeks. The 

 midline of the body is relatively insensitive. The sensivity in- 

 creases from the far extremity of the limbs towards the trunk. 

 Experiment 83. Using test tubes containing warm or cold 

 water, proceed to confirm the above statements. 



SENSE OF TOUCH. 



This is likewise mediated by spots (touch spots), which are dis- 

 tributed independently of those of temperature, and are most 

 numerous to the "windward" side of the hair follicles. 



FIG. 60. Hair aesthesiometers. 



Experiment 84. Using the same area of hand as was employed 

 for determining the temperature spots, or a part of it, make 

 an exact chart indicating the position of the hairs (use a lens for 

 this purpose). Now cut the hairs flush with the skin, by means 

 of a sharp scissors, or shave the part. Take a series of hair 

 aesthesiometers made by mounting straight hairs of varying 

 thickness at right angles on wooden holders (Fig. 60). The 

 exact weight at which each hair bends when pressed on one scale 

 pan of a balance is marked on the handle. Select a hair which 

 provides a stimulus of such a strength that it will call forth the 



