KIDNEYS 



187 



one is able to continue those exertions. The habit of lying down 

 when tired is a good one. 



The Relation of Clothing to Health. — Clothes, like the covering 

 of feathers on birds or fur on mammals, are 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 out- 

 side 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 next 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. 



It is impossible for us to form proper habits of breathing unless 

 clothing is worn loosely over the chest and abdomen. The days of 

 tight corsets and lacing seem to be over for girls, but much harm 

 is done by tight garters. We should avoid 

 tight belts or any tight clothing, as it in- 

 terferes with natural circulation. 



Organs of Excretion. — All the life pro- 

 cesses which take place in a living thing 

 result ultimately, not only in the giving off 

 of carbon dioxide, but also in the formation 

 of organic wastes within (he body. The 

 retention of the wastes which contain nitro- 

 gen is harmful to animals. In man, the 

 skin and kidneys remove these wastes from 

 the body, hence they are called the organs 

 of excretion. 



The Kidneys. — The human kidneys are 

 situated in the dorsal part of the abdominal cavity in the '' small 

 of the back " region. Each is about four inches long, two and one 



Kidney 



Ureter 



Bladder 



■Urethra 

 Kidneys and bladder ; 

 kidney in section. 



