34 HUMAN PHYSIOLOGY 



depends on the manner of stimulation, that is, whether the 

 points are stimulated simultaneously or successively. If 

 stimulated simultaneously, the distances for various parts of 

 the body are as follows: 



Tip of tongue i mm 



Tip of finger 2 " 



Lips. 4.5 " 



Forehead 22 " 



Back of hand 31 ' ' 



Upper arm and thigh 68 " 



When the points are stimulated successively the distances 

 are much smaller, being equal to the distances which sep- 

 arate the individual tactile points. For successive stimula- 

 tion, therefore, each tactile point has a special space value. 



An area of the skin in which two stimuli cannot be distinctly felt 

 is called a tactile area. The tactile areas for successive stimulation 

 are smaller than those for simultaneous stimulation. 



