240 



Hair follicle 



How a Co?nplex Animal Uses Food unit iv 



Blood vessel 



Oil gland 



Hair 



Epidermis 



Touch corpuscle 



Nerve 



Muscle which 

 moves hair 



Fat cells 



Sweat duct 



Sweat gland 



d duct 



Fig. 236 Section through skin. In which layer are blood vessels and nerves lacking? 



Why do outer layers of the epidermis die? What other structures are found below 



the epidermis? These structures are in a skin layer called the dermis. 



to two pints of water are lost daily in 

 this manner by a healthy body not en- 

 gaged in exercise. Yet ordinarily you are 

 not conscious of sweat on your skin be- 

 cause it evaporates as quickly as it comes 

 to the top of the duct. You become aware 

 of it only when it pours out more rapidly 

 than it evaporates from the surface. This 

 happens during vigorous exercise or on 

 warm days, particularly in a moist at- 

 mosphere when the evaporation of sweat 

 is slow because of the moisture in the 



air. 



Secreting cells Capillaries 



Fk;. 237 A sweat gland highly magnified. No- 

 tice the many capillaries near the secreting cells 

 of the gland. How do sweat glands help in regu- 

 lating body temperature? 



A cooling system that regulates itself. 

 Evaporation from any surface cools the 

 surface. If you spread a drop of alcohol 

 on the back of one hand and a drop of 

 water on the back of the other hand, you 

 will notice that the alcohol evaporates 

 first. You will also notice that the spot 

 that was wet with alcohol becomes 

 cooler than the spot that was wet with 

 water. Now perform a more accurate 



