A YEAR IN SCIENCE 133 



CHAPTER XXV 

 ORGANS OF SPECIAL SENSES 



Exercise 89, Cutaneous Sensations. 

 Object: A study of the sensations of touch and 

 temperature. 



Apparatus 



Metal compasses Cold water 



Hot water 



Directions: A. One pupil should operate, another 

 acting as subject. The subject should be blindfolded. 

 What is the least distance apart at which the two 

 points of the compass may be held and felt as two 

 points, when applied to the tips of the fingers ? The tip 

 of the tongue? Back of the hand? Back of the neck? 

 Record results. Are all parts of the body equally 

 sensitive to touch? Which parts are most sensitive? 



B. Dip a point of the compass in cold water and 

 move it lightly over the back of the hand. Does it 

 feel equally cold to all parts of the hand? Mark with 

 an ink dot those spots where the sensation is most 

 acute. Now dip the compass point in hot water, and 

 repeat the experiment. Locate as before, the points 

 where the sensation is most .acute. Do the hot and 

 cold spots coincide? Test other areas of the body in 

 the same way. Are all parts of the body equally 

 sensitive to temperature ? Which parts are most sensi- 



