TOUCH 



27 



Fig. 1032. Touch- 

 Corpuscle from Finger 

 Tip of Man, in section, 



numerous touch-corpuscles which underlie the little ridges seen 

 on the tips of our fingers and thumbs (fig. 1032). In Reptiles, 

 Birds, and Mammals there are also curious struc- 

 tures known as Pacinian bodies (fig. 1033), m 

 which the ending of a nerve is surrounded by a 

 series of layers arranged almost like the coats of 

 an onion. There is reason to think that these are 

 very sensitive to slight pressures. They abound, 

 for instance, in the wing-membranes of Bats, and 

 it is well known that these creatures can easily 

 steer their way in the dark through a veritable 

 maze of obstacles, such as that afforded by a 

 series of strings running in various directions. 

 Pacinian bodies are also found connected with 

 tendons, ligaments, and various internal organs. 

 The use of these is probably to apprise the central nervous 

 system of variations in pressure and tension which take place 

 as between the different parts of the body 

 itself. 



We are still very much in the dark as 

 to how far there do or do not exist special 

 end-organs which are affected by variations 

 in temperature. It is known that definite 

 spots in the human skin are sensitive to 

 such variations, but there do not appear 

 to be any special sense-organs in these 

 spots. Some of the sensory nerve-fibres 

 terminate in the skin by dividing into a 

 number of little branches which do not 

 become continuous with modified epidermal 

 cells, and it has been suggested that these 

 "free nerve endings" are related to the 

 temperature sense. . ** '33 ; -A Padman corpuscle 



1 in Longitudinal Section, enlarged. A 



While the entire external surface of the nerve-fibre ('), surrounded by a 



....... 1 sheath (./), enters the base of the 



body is sensitive to contact, pressure, and corpuscle, loses its sheath, traverses 



i . i . a central core (m). and ends in an 



changes in temperature, this is in many irregu i ar expansion (a). The cor - 



raqpq inmiffiripnt- tn prmhle the rermisite puscle is mostly made up of numerous 



me requibi te concentric fibrous layers (c> ^ 



adjustments to the environment to be 



brought about. And we accordingly find that in many animals 



organs of active touch have been evolved, which explore the 



