360 A YEAR IN SCIENCE 



a countless number of organs at the ends of nerves by 

 means of which, we receive messages of temperature 

 and touch. Third, by means of perspiration it throws 

 off a great deal of water and small quantities of other 

 waste materials. Fourth, it is the chief means of 

 regulating the temperature of the body. 



Structure. As we might infer from all of these uses, 

 the skin is a complex organ. It consists of two layers; 

 the outer is called the epidermis, and the inner the 

 dermis. 



The epidermis is formed of layers of cells. It con- 

 tains no blood vessels and hence it is possible to prick 

 this layer without causing bleeding. The growing cells 

 are at the bottom of the epidermis, where they absorb 

 nourishment from the dermis beneath. As these cells 

 grow and increase in numbers they crowd the cells 

 above away from the source of supply and they become 

 thinner and drier until they become hard scales. These 

 scales are constantly being worn and washed away. 

 Scattered among the lower cells of the epidermis are 

 some cells which contain pigment, or coloring matter. 

 An abundance of these cells gives the black color to 

 the skin of the negro. 



The dermis is composed mainly of a loose network 

 of fibrous tissue. In this are embedded numerous blood 

 vessels, nerves, sweat and oil glands, and the roots of 

 the hair. In the deeper parts of the dermis are groups 

 of fat cells. These fill up the inequalities left by the 

 tissues below the skin and make it smooth and plump. 



