~2. Bad Odors.~--Anything which rots or decays will in so doing produce an unpleasant odor. Bad odors produced in this way are very harmful and likely to make us sick. Many people have rotting potatoes and other vegetables in their cellars, and swill barrels, and heaps of refuse in their back yards. These are all dangerous to health, and often give rise to very serious disease. We should always remember that bad odors caused by decaying substances are signs of danger to health and life, and that these substances should be removed from us, or we should get away from them, as soon as possible.

~3. Germs.~--The chief reason why bad odors are dangerous is that they almost always have with them little living things called _germs_. Germs are so small that they cannot be seen by the naked eye: it takes a strong microscope to enable us to see them, but they are so powerful to do harm that if we receive them into our bodies they are likely to make us very sick, and they often cause death.

~4. Contagious Diseases.~--You have heard about diphtheria and scarlet fever and measles, and other "catching diseases." When a person is sick with one of these diseases, the air about him is poisoned with germs or something similar, which may give the same disease to other persons who inhale it. So when a person is sick from one of these diseases, it is very important that he should be put in a room by himself and shut away from every one but the doctor and the nurse. It is also necessary that all the clothing and bedding used by the sick person, and everything in the room, as well as the room itself, should be carefully cleansed and disinfected when the person has recovered, so as to wipe out every trace of the disease. The writer has known many cases in which persons who have been sick with some of these diseases were careless and gave the disease to others who died of it, although they themselves recovered. Do you not think it very wrong for a person to give to another through carelessness a disease which may cause his death?

~5.~ Unhealthful vapors and odors of various sorts arise from cisterns and damp, close places under a house. Rooms which are shaded and shut up so closely that fresh air and sunshine seldom get into them should be avoided as dangerous to health.

~6. Breath-Poisoned Air.~--The most dangerous of all the poisons to which we are exposed through the air are those of the breath, of which we learned in a preceding lesson. We need plenty of fresh air to take the place of the air which we poison by our breath. Every time we breathe, we spoil at least _half a barrelful of air_. We breathe twenty times a minute, and hence spoil ten barrels of air in one minute. How many barrels would this make in one hour? We need an equal quant.i.ty of pure air to take the place of the spoiled air, or not less than ten barrels every minute, or _six hundred barrels every hour_.

~7. Ventilation.~--The only way to obtain the amount of fresh air needed, when we are shut up in-doors, is to have some means provided by which the fresh air shall be brought in and the old and impure air carried out. Changing the air by such means is called _ventilation_.

Every house, and especially every sleeping-room, should be well ventilated. School-houses, churches, and other places where many people gather, need perfect ventilation. Ask your teacher to show you how the school-room is ventilated; and when you go home, talk to your parents about the ventilation of the house in which you live.

~8.~ Many people ventilate their houses by opening the doors and windows. This is a very good way of ventilating a house in warm weather, but is a very poor way in cold weather, as it causes cold draughts, and makes the floor cold, so that it is difficult to keep the feet warm. It is much better to have the air warmed by a furnace or some similar means, before it enters the rooms. There ought also to be in each room a register to take the foul air out, so that it will not be necessary to open the windows. This register should be placed at the floor, because when the pure air enters the room warm, it first rises to the upper part of the room, and then as it cools and at the same time becomes impure, it settles to the floor, where it should be taken out by the register.

~9. How to Breathe.~--We should always take pains to expand the lungs well in breathing, and to use the entire chest, both the upper and the lower part. Clothing should be worn in such a way that every portion of the chest can be expanded. For this reason it is very wrong to wear the clothing tight about the waist. Clothing so worn is likely to cause the lungs to become diseased.

~10. Bad Habits.~--Students are very apt to make themselves flat-chested and round-shouldered by leaning over their desks while writing or studying. This is very harmful. We should always use great care to sit erect and to draw the shoulders well back. Then, if we take pains to fill the lungs well a great many times every day, we shall form the habit of expanding the lungs, and shall breathe deeper, even when we are not thinking about doing so.

~11. Breathing through the Nose.~--In breathing, we should always take care to draw the air in through the nose, and not through the mouth. The nose acts as a strainer, to remove particles of dust which might do harm if allowed to enter the lungs. It also warms and moistens the air in cold weather. The habit of breathing through the mouth often gives rise to serious disease of the throat and lungs.

~12. Effects of Alcohol and Tobacco upon the Lungs.~--Both alcohol and tobacco produce disease of the breathing organs. Smoking injures the throat and sometimes causes loss of smell. Serious and even fatal diseases of the lungs are often caused by alcohol.

~13.~ Many people suppose that the use of alcohol will save a man from consumption. This is not true. A man may become a drunkard by the use of alcohol, and yet he is more likely to have consumption than he would have been if he had been a total abstainer. "Drunkard's consumption" is one of the most dreadful forms of this disease.

SUMMARY.

1. Pure air is as necessary as food and drink.

2. Anything which is rotting or undergoing decay causes a bad odor, and thus makes the air impure.

3. Foul air contains germs which cause disease and often death.

4. Persons sick with "catching" diseases should be carefully avoided.

Such persons should be shut away from those who are well, and their rooms and clothing should be carefully cleansed and disinfected.

5. The breath poisons the air about us. Each breath spoils half a barrelful of air.

6. We should change the air in our houses, or ventilate them, so that we may always have pure air.

7. We should always keep the body erect, and expand the lungs well in breathing.

8. The clothing about the chest and waist should be loose, so that the lungs may have room to expand.

9. Always breathe through the nose.

10. Tobacco causes disease of the throat and nose.

11. Alcohol causes consumption and other diseases of the lungs.

CHAPTER XV.

THE SKIN AND WHAT IT DOES.

~1. The Skin.~--The skin is the covering of the body. It fits so exactly that it has the precise shape of the body, like a closely fitting garment. If you will take up a little fold of the skin you will see that it can be stretched like a piece of india-rubber. Like rubber, when it is released it quickly contracts and appears as before.

~2. The Bark of Trees.~--Did you ever peel the bark off of a young tree?

If so, you have noticed that there were really two barks, an outer bark, as thin as paper, through which you could almost see, and an inner and much thicker bark, which lay next to the wood of the tree. You can peel the outer bark off without doing the tree much harm. Indeed, if you will notice some of the fruit or shade trees in the yard, at home, you will see that the outer bark of the tree peels itself off, a little at a time, and that new bark grows in its place. If you tear off the inner bark, however, it will injure the tree. It will make it bleed, or cause the sap to run. The sap is the blood of the tree. The bark is the skin of the tree. When the bare place heals over, an ugly scar will be left.

~3. The Cuticle.~--Our bodies, like trees, have two skins, or really one skin with an outer and an inner layer. When a person burns himself so as to make a blister, the outer skin, called the _cuticle_, is separated from the inner by a quant.i.ty of water or serum poured out from the blood. This causes the blister to rise above the surrounding skin. If you puncture the blister the water runs out. Now we may easily remove the cuticle and examine it. The cuticle, we shall find, looks very much like the skin which lines the inside of an egg-sh.e.l.l, and it is almost as thin.

~4.~ The cuticle is very thin in most parts of the body, but in some places, as the palms of the hands and the soles of the feet, it is quite thick. This is because these parts of the skin come in contact with objects in such a way as to be liable to injury if not thus protected.

The cuticle has no blood-vessels and very few nerves. With a fine needle and thread you can easily take a st.i.tch in it without making it bleed or causing any pain.

~5. The Pigment.~--The under side of the cuticle is colored by little particles of pigment or coloring matter. The color of this pigment differs in different races. In the negro, the color of the pigment is black. In some races the pigment is brown. In white persons there is very little pigment, and in some persons, called albinos, there is none at all.

~6. The Inner or True Skin.~--The inner skin, like the inner bark of a tree, is much thicker than the outer skin. It is much more important, and for this reason is sometimes called the _true skin_. It contains nerves and blood-vessels.

[Ill.u.s.tration: SKIN OF PALM OF HAND MAGNIFIED.]

~7. The Sweat Glands.~--If you look at the palm of the hand you will see many coa.r.s.e lines, and by looking much closer you will see that the palm is completely covered with very fine ridges and furrows. Now, if you examine these ridges with a magnifying-gla.s.s, you will find arranged along each ridge a number of little dark spots. Each of these points is the mouth of a very small tube. This is called a _sweat duct_. These ducts run down through both the outer and inner layers of the skin. At the under side of the true skin the end of the tube is rolled up in a coil, as you can see by looking at the ill.u.s.tration on the following page. The coiled parts of the tubes are called _sweat glands_, because they separate from the blood the fluid which we call sweat or perspiration.

~8. The Oil Glands.~--There are other little glands in the skin which make fat or oil. The oil is poured out upon the skin to keep it soft and smooth.

[Ill.u.s.tration: THE STRUCTURE OF THE SKIN.]

~9. The Hair.~--There are some curious little pockets in the skin. Out of each of these pockets grows a hair. On some parts of the body the hairs are coa.r.s.e and long; on other parts they are fine and short.

~10.~ Many of the ducts leading from the oil glands open into the pockets or pouches from which the hairs grow. The oil makes the hair soft and glossy. Nature has thus provided an excellent means for oiling the hair.

~11.~ The hair is chiefly useful as a protection. It is also an ornament.

~12. The Nails.~--The nails of the fingers and the toes grow out of little pockets in the skin just as the hairs do. Both the hair and the nails are really parts of the outer skin, which is curiously changed and hardened. The nails lie upon the surface of the true skin and grow from the under side as well as from the little fold of skin at the root of the nail. They are made to give firmness and protection to the ends of the fingers and toes. The nails of the fingers are also useful in picking up small objects and in many other ways.

~13. Uses of the Skin.~--The skin is useful in several ways:

(1) _It Removes Waste._--The sweat glands and ducts are constantly at work removing from the blood particles which have been worn out and can be of no further use. If we get very warm, or if we run or work very hard, the skin becomes wet with sweat. In a little while, if we stop to rest, the sweat is all gone. What becomes of it? You say it dries up, which means that it has pa.s.sed off into the air. Sweating is going on all the time, but we do not sweat so much when we are quiet and are not too warm, and so the sweat dries up as fast as it is produced, and we do not see it. Nearly a quart of sweat escapes from the skin daily.

(2) _Breathing through the Skin._--We breathe to a slight extent through the skin. There are some lower animals which breathe with their skins altogether. A frog can breathe with its skin so well that it can live for some time after its lungs have been removed. Breathing is an important part of the work of the skin, and we should be careful, by keeping it clean and healthy, to give it a good chance to breathe all that it can.

(3) _The Skin Absorbs._--The skin absorbs many substances which come in contact with it, and hence should be kept clean. If the foul substances which are removed in the sweat are allowed to remain upon the skin, they may be taken back into the system and thus do much harm.

(4) _The Skin has Feeling._--When anything touches the skin we know it by the feeling. We can tell a great many things about objects by feeling of them. If we happen to stick a pin into the skin we feel pain. We are also able to tell the difference between things which are hot and those which are cold. Thus the sense of feeling which the skin has is very useful to us.