The nails are not poisonous, but the dirt under them may be. We ought to keep them clean. Clean nails are one mark of a careful boy or girl.
126. Hair.—Some of the scales of epithelium over some parts of the body dip into tiny holes in the skin. In each hole they become matted together to form a hair. Fine short hair grows on almost every part of the body. On the top of the head it grows long and thick. When boys become men, it also grows long upon their faces. The skin pours out a kind of oil to keep the hair soft and glossy.
A hair (×200).
a the surface of the skin.
b a hair.
c an oil gland.
d a muscle to make the hair stand on end.
e and g, the growing cells of the hair.
f fat in the skin.
127. Care of the hair.—The hair may become dirty like any other part of the body. Brushing it takes out a great deal of dirt, but you should also wash it once a week.
The oil in the skin ought to be enough for the hair. Hair oils do not do the hair any good. If you wet the hair too often, you may make it stiff and take away its gloss. It is best to comb the hair dry. Brush it so as to spread the oil of the skin. Hair dyes are poisonous, and ought not to be used.
128. The sweat or perspiration.—The scales of epithelium dip into the skin and there line tiny tubes. The tubes form the sweat, or perspiration, out of the blood. The tubes are too fine to be seen, but they are upon almost every part of the body. They take the ashes or other waste matter or poisons from the blood and wash them out of the tubes with the perspiration. So the perspiration has two uses. First, it takes heat away from the body (see § [108]). Second, it gets rid of the waste matters or ashes of the body. It has very little of these at any one time, but in a day it gets rid of a great deal.
129. The kidneys.—The kidneys are close to the backbone, below the heart. They are made of tiny tubes much like the sweat tubes in the skin. The tubes take ashes and other waste matters from the blood, also a great deal of water. They also take away poisons and disease germs when we are sick. The kidneys take away about as much water as the skin, but they get rid of very much more poisons and waste matters than the skin does. If our kidneys should stop their work, we should soon die.
130. Need of bathing.—When the perspiration dries from the skin, it leaves the waste and poisons behind. We cannot always see the dried matters, but they always have an unpleasant odor. We should bathe often enough to keep our body from having an unpleasant smell. We should wash the whole body with soap and hot water at least once a week in winter and more often than that in summer.