DERMIS. 63 



matter. In those of brunette or dark complexion, this 

 pigment is more abundant. In negroes there is a large 

 amount of it. 



Exposure to the air and to sunlight increases the quan- 

 tity of coloring matter in the epidermis. Hence the 

 skin darkens or " tans." If the whole thickness of the 

 epidermis is destroyed, by a burn or wound, the deepest 

 cells of the new epidermis do not usually form any color- 

 ing matter; therefore scars remain white, even in negroes. 



8. Redness of the Skin and blushing are due not to 

 changes in the epidermis, but in the dermis, which be- 

 comes fuller of blood. The red blood is then seen 

 through the epidermis. Constant pallor or great white- 

 ness of the skin, is a sign that there is not enough blood 

 flowing in the dermis; it is usually an indication of dis- 

 ease. Some persons are pale from infancy and neverthe- 

 less healthy; but they are exceptional. 



9. The Dermis consists of a close network of connec- 

 tive tissue, containing in its meshes many nerves, and 

 numerous tubes filled with blood, named blood-vessels. 

 It is the nerves (Chap. XVIII.) which give it feeling. 

 When hides are tanned, the dermis is turned into leather. 

 Its outer surface, next the epidermis, is not smooth, but 

 presents numerous tiny projections, named papilla. In 

 Fig. 21 is shown a papilla containing a knot of blood- 

 vessels. Other papillae contain nerves instead of blood- 

 vessels, and are concerned in the feeling of touch. On 

 the palm of the hand, the papillae of the dermis are 



8. What is the cause of redness of the skin ? Of pallor ? Is con- 

 stant pallor always a sign of disease ? 



9. Of what is the dermis composed ? What are its papillae? What 

 do different papillae contain ? How are the fine ridges and furrows of 

 the palm produced ? What causes the deep lines of the palm ? 



