ORGANS OF TOUCH. 201 



smell are much less vitiated, than in civilized man ; and 

 hence the men of the forest, it is said, are guided, in a 

 considerable degree by these senses, in the choice of their 

 food, especially in times of scarcity, when they are obliged 

 to roam in search of new articles. 



ORGANS OF TOUCH. 



628. By the sense of touch, we are enabled to know the 

 external properties of bodies. 



Physiologists make a distinction between tact and touch. 

 Tact, with some few exceptions, is generally diffused 

 through all our organs, and particularly over the skin. It 

 exists in all animals, while touch exists chiefly in the 

 fingers of man, in the antenna of insects, and in the ndses 

 of certain quadrupeds. 



629. In the exercise of these functions, tact is considered 

 passive, as when any part of the system comes into contact 

 with another body, a sensation of its presence is given, 

 without the exercise of volition. Oa the contrary, touch 

 is active, and is exercised voluntarily for the purpose of con- 

 veying to the mind a knowledge of the qualities, or proper- 

 ties of the surfaces of bodies ; as when we feel a piece of 

 cloth to ascertain its qualities, or a polished surface to 

 prove its smoothness. 



630. Anatomy of the Skin. The sensation of tact and 

 touch is conveyed to the brain by means of nerves situated 

 in the skin. 



The skin consists of three parts, called the cuticle, or 

 epidermis ; the rete mucosum ; and the corium, or cutis 

 vera, or true skin. 



The cuticle is the external layer. In its structure it is 

 membranous and dry, having neither nerves, veins, nor 

 arteries. It has, therefore, no sensation, its office being 

 merely to protect the true skin from external injury. 



What is the difference between touch and tact? In the exercise of these 

 functions, which is active and which passive? How are these sensations 

 conveyed to the brain? What parts compose the skin, and what their 

 names ? What is the cuticle and where is it situated ? What is the use 

 of the cuticle ? 



