146 



HUMAN BIOLOGY 



Fig. 120. — Different Kinds of Touch 

 Bodies at Ends of Nerves. 



A, from cornea of the eye ; B, from the tongue of a 

 duck ; C, D, E, from the skin of the fingers. (Jegi.) 



the skin that is touched. A lighter pressure can be felt 

 on the forehead and temples than with any part of the 



body. (Why is it best 

 for this to be the 

 case ?) The greatest 

 delicacy in locating 

 the point of the skin 

 touched is found to be 

 tocated in the tip of 

 the tongue, the lips, 

 and the ends of the 

 fingers (Exp. 1). 

 (Why is it best that 

 this is so ?) This deli- 

 cacy is least in the 

 middle of the back. 

 The delicacy varies 

 with the number of touch corpuscles in different parts 

 of the skin. The sense of touch is capable of great 

 cultivation, as in the case of the blind. 



The temperature sense is given by special nerves called the thermic 

 nerves (Exp. 2). That the thermic nerves are easily fatigued is noticed 

 soon after entering a bath of hot water; it is also shown by the fact 

 that in cold countries the nose or ears of a person may freeze without 

 his feeling it. 



The Muscular Sense. — The special sense of touch gives some sense of 

 weight. A weight upon the skin must be increased by one third before 

 it feels heavier, but by lifting an object so as to bring into action the 

 muscular sense residing in nerves ending in the muscles an increase of 

 only one seventeenth of the original weight can be noticed (Exp. 3). 

 This sense gives us a continual account of the position of the limbs 

 (Exp. 4). 



The end organs of taste are located in the papillae of 

 the tongue. The tongue has a fuzzy look because of the 

 numerous papillae. 



