316 HOW DOES THE HUMAN MACHINE DO ITS WORK? 



PROBLEM n. WHAT IS THE STRUCTURE OF THE SKIN? 



Laboratory Exercise. To find out some functions of the skin. 



Hand lens. Ether or alcohol. Large glass jar. Two thermometers. 

 Model or illustration showing section of skin. 



Find out whether all parts of the skin of the arm are equally sensi- 

 tive, by touching various parts of it with the sharp point of a pencil. 

 Cool a large glass jar, and hold the hand and wrist in the jar for a few 

 moments, closing the opening of the jar with a cloth or a towel. What 

 collects on the inner surface of the jar? 



What happens when you take violent exercise? Weigh yourself 

 before and after a period of hard work in the gymnasium. Is there 

 any loss in weight ? How do you account for it ? 



Place a few drops of ether or alcohol on the back of your hand and 

 note the evaporation of the liquid. What sensation do you feel while 

 the evaporation takes place? 



Study the model or diagram of skin on page 17. Locate the two 

 layers. Find and describe the sweat glands, oil glands, and sense 

 organs. Draw a diagrammatic sketch of the model and label all 

 parts. Write a statement giving the functions of each part. 



Conclusions. Is the skin an organ of sensation? What passes off 

 through the skin? What effect on your bodily comfort does this last 

 function have? 



The skin. Covering the body „is the protective structure 

 called the skin. Under the epidermis, a layer of dead cells, there 

 are delicate sense organs, lying in the dermis or true skin, which 

 give us sensations of touch, pressure, and temperature. The skin 

 aids also in passing wastes out of the body by means of sweat 

 glands, and it plays an important part in equalizing the tempera- 

 ture of the body. 



Nails and hair. Nails are outgrowths of the horny layer of the 

 epidermis. A hair is also a growth of the epidermal layer, although 

 it is formed in a deep pit or depression in the dermis ; this pit is 

 called the hair follicle. 



The glands of the skin. Scattered through the dermis, and 

 usually connected with the hair follicles, are tiny oil-secreting 

 glands, the sebaceous (se-ba'shus) glands. The secretion of these 

 glands keeps the hair and surface of the skin soft and. pliable. 

 The other glands in the dermis, known as sweat glands, are to be 

 found in profusion, over 2,500,000 being present in the skin of a 

 normal man. These glands excrete certain wastes from the blood 

 in the water they pass off. 



