TOUCH. 147 



Do the nerves of special sense possess the property of common 

 sensibility ? 



No. The special nerves have no other function than the special 

 one for which they are set apart ; and when they are separated 

 from their special organs for receiving impressions, they no longer 

 respond to the customary stimuli. 



What are the special senses? 



Touch, taste, smell, hearing, and sight. 



TOUCH. 

 What is the organ of touch ? 



The skin and the mucous membranes adjoining it. The nails 

 and teeth too exercise a peculiar function in this regard, and the 

 hair in some regions e. g. eyelashes. The sensations of touch are 

 communicated to the central nervous system through the agency 

 of the sensory nerves of the spinal and cranial systems. 



What varieties of the sense of touch are found ? 



(1) Tactile sensibility, or touch proper ; (2) the sense of pressure 

 or weight ; (3) the sense of temperature. All of these, when car- 

 ried beyond moderate limits, are merged into the sensation of pain. 



What factors determine the acuteness of touch ? 



The distribution of the end-organs of the sensory nerves varies in 

 different parts of the body, and the more numerous the touch-cor- 

 puscles, the more acute the sensibility of the part. Again, the 

 thickness of the epidermis has marked influence in determining the 

 tactile ability, portions of the hands and feet, when callous, having 

 very blunted sensibility. 



What qualities of bodies are determined by touch ? 



Their hardness and elasticity, the quality of the surface as to 

 smoothness, the size and form and the temperature and wet or dry 

 condition, are all easily determined by touch. 



Why is the hand of especial value as an organ "of touch ? 



Because of the acuteness of its sensibility. Further than this, 

 it is so constructed as to be capable of forming impressions of 

 bodies by reason of its power to grasp them and to test them as 

 to weight. 



