158 PHYSIOLOGY. 



that it may more effectually serve as a shield to the parts it 

 covers. As the cuticle is constantly renewed from its inter- 

 nal surface, it is also constantly peeling off in the form of a 

 fine powder, or thin scales. After scarlet fever, and other 

 diseases, attended with great heat of the skin, it is entirely 

 removed ; the old scarf-skin, as it is called, being thrown off 

 in large patches. We find a cuticle in all organized beings, 

 plants, as well as animals, though it differs greatly in struc- 

 ture and appearance. In many reptiles and crustaceous 

 animals it is entirely shed at certain periods, presenting an 

 exact mould of their bodies, their scales, and other external 

 parts, and even their eyes being exactly represented. 



7. The mucous web has already been pretty fully described. 

 It is a soft pulpy net-work, and seems to consist chiefly of 

 the shaggy extremities of blood-vessels, interlaced and bound 

 together by delicate filaments of cellular membrane. ) It is 

 the seat of those minute globules which constitute the colour- 

 ing matter which vary in their tints in different races. 

 These tints are influenced in a greater or less degree by 

 climate, for we find in tropical countries the colours of both 

 plants and animals are more intense and brilliant than in 

 colder regions, and that exclusion from light produces a pale 

 blanched appearance, while exposure to it has a contrary 

 tendency ; but these variations are neither permanent nor 

 do they descend to the offspring. 



8. The dermis, or true skin, is the thickest part of the 

 external integuments, and is composed of an infinite number 

 of plates, consisting of filaments inextricably wound together, 

 and abundantly supplied with blood-vessels and nerves J The 

 external surface of the cutis is every where studded by very 

 minute nipples or papillae, and in several parts, as the palms 

 of the hands and the ends of the fingers, they are arranged 

 in symmetrical rows, which form wavering lines, and separ- 

 ated by small crevices that admit of the flexions of the skin 

 and its adaptation to the surfaces of external objects.| These 

 papillae are the terminations of nerves and blood-vessels, and 



