SENSE ORGANS. 



20I 



case of papillae each one contains a tactile bulb. A sen- 

 sory fiber enters and terminates in each bulb. These 



are therefore end organs or 

 terminals. The epidermis 

 proper is not sensitive; it 

 only protects the sensitive 

 dermis from too rude con- 

 tact. 



Minimum Tactile. — 

 -n We have already alluded 

 to this subject in compar- 

 ing sight with touch (page 



FIG. 12 8.-Tactilecorpuscles : A, from ^^ We re P eat jt heI " e in 

 the finger of a man ; B, from the its proper Connection. If 

 skin of a bird: n, nerves. (After ■ r , • •, , , 



wiedersheim.) a P alr of dividers be opened 



widely and the skin be 

 touched with the points (blunted a little so that they do 

 not prick) we feel two distinct impressions. If we now 

 bring the points nearer and nearer together, repeating 

 the experiment until we feel but one impression, the 

 nearest distance apart that we can still 

 feel two impressions is called the mini- 

 mum tactile. It is a measure of capacity 

 to give definite knowledge by touch. 

 It differs greatly in different parts of 

 the skin. On the middle of the back 

 it is about three inches, on the arm or 

 back of the hand about one half to 

 three quarters of an inch, on the finger 

 tips about one twelfth of an inch, on 

 the tip of the tongue about one twenty- 

 fourth of an inch, or one millimetre. 



Double Tactile Images. — There 

 is here also a kind of double images comparable to the 

 double images of sight. If the middle finger be crossed 



Fig. 129. 



