318 HOW DOES THE HUMAN MACHINE DO ITS WORK? 



be covered at once with a paste of baking soda, with olive oil, or 

 with a mixture of limewater and linseed oil. These tend to lessen 

 the pain by keeping out the air and reducing the inflammation. 



The relation of clothing to the skin. Clothes are primarily for 

 protection. They may be classed as either good or bad conductors 

 of heat. Good heat conductors, such as linen or cotton, allow the 

 temperature outside of them to replace that of the layer of air 

 directly around the body, while silk and wool are poor conductors 

 and protect the body from a lower temperature outside. Warmth 

 of clothing is largely dependent on the amount of air held between 

 its fibers. Cool clothes have little air space in the meshes of the 

 cloth, while loosely woven underclothes are warmer because they 

 absorb perspiration rapidly and dry out quickly. Hence they 

 do not feel cold or clammy to the perspiring skin as linen and 

 cotton do. Young people can wear linen or cotton underclothes 

 safely all the year round if they make proper changes in the weight 

 of their outside garments. Older persons, on the other hand, need 

 to wear woolen underclothes in the winter because these keep out 

 cold and absorb perspiration without chilling the skin. 



Self-Testing Exercise 



The skin is composed of (1) layers, the (2) and 



(3), the latter is the (4) layer and is largely (5) . 



The skin excretes certain wastes through the (6) glands. An 



open wound may become infected by (7) which cause 



(8) . Boils are an example of an (9) by (10) . 



The skin is a (11) covering consisting of the epidermis, a layer 



of (12) (13), and the living (14) which con- 

 tains the (15) and (16) glands, (17) 



(18), (19), and (20) (21). 



PROBLEM m. WHAT IS THE RELATION OF MUSCLES TO 



BONES? 



Laboratory Exercise. To study the use of the muscles and bones. 



Frogs preserved in formalin, mounted skeletons of frog, manikin, 

 human skeleton, or good diagram. 



Note the " flesh " forming the muscle of the leg. (A muscle is 

 attached to the bone by a tough tendon.) 



Holding your leg still, raise the foot up and down. Where do you 

 feel the contraction of the muscle? Referring to the manikin, deter- 



