NATURAL HISTORY. 15 



" Vast chai* of being ! which from God began, 

 Natures etherial, human, angel, man." POPE. 



nail is embedded in a fold of sensitive skin to the depth of about a twelfth part of an 

 Inch for the fingers and toes, about the eighth part of an inch for the thumb, and 

 the sixth of an inch for the great toe. 



31. What are the papilla? 



Papillae arc the terminations of the nerves on the surface of the 

 skin, soft and pulpy, and forming minute protuberances, resembling 

 the nap of frieze cloth, though greatly inferior in magnitude. These 

 nerves are a species of animal feelers, and are the immediate 

 instruments of sensation. 



32. When examining 1 or enjoying any object, it is natural to enquire, What are the 

 Changes produced in the nervous papillae or organs of sensation 1 If an object 

 possessed of agreeable feeling is perceived, the nervous papilla; instantly extend 

 themselves, and from a state of flaccidity become comparatively rigid. When a 

 person in the dark inclines to examine any object, in order to discover its figure or 

 other qualities, he perceives a kind of rigidity at the tips of his fingers. If the 

 fingers are kept long in this state the rigidity of the nervous papillae will give him 

 a kind of pain or anxiety, which is caused by the over distention of the papillae. 

 If a small insect creep upon a person's hand, when the papillae are flaccid, ita 

 movements are not perceived ; but if he happen to direct his eye to the aidmal, he 

 immediately extends the papillae, and feels distinctly all the motions of the insect. 



33. Why is the cuticle slightly rough, instead of being perfectly 

 smooth t as might be hastily considered its most appropriate 

 characteristic ? 



Because the slightly rough surface endows it with a quality more 

 adapted to convey sensation. An illustration of this truth is fur- 

 nished by the imperfect sense of touch which contact with polished 

 surfaces affords, as compared with the handling of rough bodies. 



34. A provision for increasing friction is especially necessary in some parts of the 

 skin. Thus the roughness of the cuticle in the palm of the hand, and in the sole of 

 tb foot, gives us a firmer grasp and a steadier footing. Nothing is so little apt to 

 gb.p as the thickened scarf-skin, either of the hand or the foot. 



35. Why has the skin a purple hue when exposed to cold ? 



Because the vigour of the nervous power is reduced by cold ; and 

 in addition to the repulsion inward of most of the blood contained 

 within the vessels of the skin producing pallor, that which remains 



