ELEMENTARY PHYSIOLOGY 



we are made aware of certain conditions of various parts of the 

 body. 



The following example will help to make this distinction 

 clear : The point of a needle is pressed against the skin. A 

 sensation is at once experienced. This sensation is that of touch, 

 and is at once referred to an external object. But if the needle 

 is made to penetrate beneath the epidermis, a sensation of pain 

 is produced, which continues after the needle has been withdrawn. 

 The pain is no longer referred to an external object, but reveals 

 to us a changed condition in a particular part of the body. 



Fig. 176. A Nerve 

 of the Finger, with 

 Pacinian Bodies Fl S- I77- Section of a Papilla of the Skin, 

 attached. Natural showing a Touch Corpuscle. Highly 



size. magnified. 



t, tactile or touch corpuscle ; d, nerve fibres 

 passing up to it. 



The sense of touch may be regarded as a modification of com- 

 mon sensation ; and all parts of the body which are supplied with 

 sensory nerves are to a certain extent organs of touch ; but this 

 sense is perfected only in the skin, tongue, and lips. 



The sensibility of the skin is due to the presence of nerve 

 fibres distributed through the dermis. Some of these nerve fila- 

 ments subdivide in the skin, and possibly terminate in individual 

 cells ; but many of them, especially in the more sensitive parts of 

 the skin, end in minute bodies of various forms. 



