PROBLEM 5. How the Body Gets Rid of Wastes 



experiment by doing Exercise 4. The 

 liquid evaporating from the skin takes 

 heat awav from the skin and, of course, 

 from the blood in the capillaries just be- 

 neath the surface. Thus the body cools 

 off. When sweat no longer evaporates, 

 your body becomes hot, that is, your 

 body temperature rises. This is some- 

 times the immediate cause of fever; the 

 sweat glands are not working properly 

 and heat is not lost. But when your body 

 is normal there is constant evaporation of 

 water and constant loss of heat. More- 

 over, the body automatically regulates 

 or varies the amount of heat lost. Regu- 

 lation of heat loss is very important to 

 good health. How is it done? 



You know from experience that when 

 you are exercising and large amounts of 

 heat are being released in your body, or 

 M'hen the temperature of the air around 

 you is very high, the skin looks red. This 

 is an indication that more blood than 

 usual is in your skin; the capillaries there 

 are filled to capacity. The more blood 

 that passes the cells of the sweat glands, 

 the more chance there is for these cells 

 to take out water and salts. Sweat flows 

 freely. As a result there is much evapo- 

 ration, and more heat is lost. At the same 

 time some heat is lost directly from the 

 skin by what is called radiation. As the 

 blood begins to cool off your skin looks 

 less red. Evidently less blood is flowing 

 through the skin. As less blood flows 

 past the sweat glands there is less secre- 

 tion of sweat. The rate of evaporation 

 becomes less, and less heat is lost. All 

 this happens without your planning or 

 thinking about it. The nervous system 

 automatically regulates the size of the 

 small blood vessels in the skin and thus 



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the amount of blood that flows through 

 the vessels. You should be able to apply 

 this information in formulating some 

 good health rules. Exercises 5 and 6 will 

 help. 



The skin functions in several other ways. 

 Exercise 7 will demonstrate one inter- 

 esting way in which the skin functions. 

 A careful study of the diagram will also 

 teach you much about your skin. You 

 may not think of the skin as an organ 

 because it is not concentrated in one 

 mass. Spread out over the whole surface 

 of the body it measures in a person of 

 average size about one and a half square 

 yards. But it is an organ just as much as 

 the stomach or heart or lungs because it 

 consists of a group of tissues that per- 

 forms some definite work. The outer 

 tissue of the skin is the epidermis. It con- 

 sists of many layers of cells. The outer- 

 most layer of epidermal cells, which is in 

 constant contact with the air, is con- 

 stantly drying up. As the protoplasm dies 

 these outer cells become hard, thus af- 

 fording protection to the various tissues 

 underneath. Being dry, the cells tend to 

 rub off, but new ones are being formed 

 continually through the division of the 

 active cells underneath. Wherever these 

 dead cells heap up in unusual amounts a 

 callus is formed. 



Under the epidermis lies a much 

 thicker layer called the dermis. Both 

 dermis and epidermis are forms of epi- 

 thelium tissue. In this layer are found 

 structures of various kinds such as the 

 roots of the hairs deep down in the der- 

 mis; the tiny bands of muscle attached 

 to the hair which by contracting make 

 the hair stand straight up, and cause 

 what you call "goose pimples"; the oil 



