bath for removing this accumulation is a warm bath; it should be taken at night, if possible. Warm baths taken in the daytime, unless they are followed by a cold shower bath, or by a dash of cold water, may make one liable to colds (cf. § 391). A warm bath at night also aids in bringing on a good night's sleep.

In the morning, when we wish to be aroused for the day's work, especially if we must go out into the cold, a cold bath is the best. The cold water gives the body a shock, in which the blood is driven inward from the skin; but after a vigorous rubbing the skin glows. This is due to the "reaction," as the blood re-enters the skin.

Many persons cannot endure the shock of a tub of cold water; they do not have a proper reaction, and feel chilly. Such persons can, as a rule, take a cold "sponge" bath, in which the water is applied rapidly with a wet sponge or washcloth. Vigorous rubbing with a dry, rough towel will bring about the "reaction."

396. Summary.-The blood carries oxygen and digested food to the cells, distributes the body's heat, and acts as the sewer for cell wastes. The organs of circulation are the heart, arteries, veins, and capillaries; also the spaces containing the lymph.

The heart has 4 chambers, each of which can be made smaller by the contraction of strong muscles.

The right auricle receives blood from the body circulation, and forces it into the right ventricle. This, in its turn, forces the blood to the lungs to be oxidized.

The left auricle receives purified blood from the lungs, and forces. it into the left ventricle. This forces it, through the artery called the aorta, into the body circulation.

The valves of the heart make the blood flow in one direction. Arteries carry blood from the heart; veins carry it to the heart; capillaries carry it from arteries to veins through the body's tissues. Arteries have very elastic walls, and are very strong. Some veins have valves that open toward the heart; the circulation in such veins is helped by the pressure of muscles near them.

The blood consists of the plasma and corpuscles. Corpuscles are red, and white. Red corpuscles contain hemoglobin, which combines

with oxygen at the lungs. White corpuscles are like amebas. They destroy bacteria.

The coagulated material of a blood clot, which closes a wound, is fibrin, formed out of one of the proteids of the blood.

Lymph is a form of blood that exists outside of the organs of rapid circulation. It has no red corpuscles. In supplying the cells, the capillaries give their food material to the lymph, and this gives it to the cells.

Excretion is the secretion of waste solutions, so that they may be removed from the body. The chief excreting organs are the kidneys. The skin excretes waste in the perspiration.

Respiration brings oxygen to the blood, and removes carbon dioxide from the blood.

The chief organs of respiration are the two lungs and the air passages. The pleurae are sacs that surround the lungs. The lungs contain a multitude of air cells.

In the lungs the air loses about 4 of its oxygen, and takes up carbon dioxide in its place.

In inspiration the chest is enlarged, and the outside air rushes into the lungs.

In expiration the diaphragm and ribs are crowded against the lung cavity, and force out the air.

The air passages include the nasal passages, the pharynx, the larynx, the trachea, and the bronchial tubes. All are lined with mucous membrane.

The larynx contains the vocal cords. In speaking and singing we make sounds with the throat, tongue, lips, teeth, and nostrils, as well as with the vocal cords.

We should have good habits of breathing, and should breathe good air. Mouth breathing is dangerous.

Colds, tobacco, alcohol, and tight clothing are all sources of danger to the organs of respiration.

The skin consists of epidermis and dermis. The sense of touch is in the papillae of the dermis.

Perspiration is secreted (excreted) by the sweat glands of the

dermis.

Hair and nails are special forms of epidermis; they grow from pits ("roots") in the dermis.

The functions of the skin are to cover the body, to assist in the sense of touch, to excrete perspiration, and to help regulate the body's temperature.

Bathing restores to the skin a fresh, clean surface, so that it can carry out its functions.

1. With what organs of speech do you make the sounds of k, l, g, d, t, m, s, and f? Find out how you make the sounds of all the letters of the alphabet, and make a list of them, putting together all the letters. that seem more or less alike.

2. If you feel chilly, a few deep breaths, especially if you "hold your breath" while the lungs are full, will make you warm. Tell why.. 3. Why should one go to bed when he has a bad cold?

4. What harm is done by the wearing of tight belts?

5. What is the danger in the taking of a hot bath, and then going: out into the cold air? How may the danger be made less?

6. What are the uses of the finger nails?

7. How can a person's finger prints be used in identifying him?

8. Why is nasal catarrh so common a disease?

9. How does a dog cool his body when he is hot?

10. Alcohol drives the blood into the skin, giving a temporary feeling of warmth. Is a drinker wise in "fortifying" himself with liquor before going out into the cold?

11. Tramps often keep themselves warm in cold weather by putting a sheet or two of newspaper inside their coats; explain. How could you use this fact to keep yourself warm, if you found the bedding of your room insufficient?

CHAPTER XIX

THE NERVES AND THE SENSE ORGANS

398. The Nervous System.- In studying a complex structure like the human body, we need to consider it part by part, and system by system. We must remember, however, that the body is not simply one structure added to another, but that it is a complete organism, with many parts acting together harmoniously. The eye, hand, and foot have each a separate function, but all can combine to do one thing, say, to make a "drop kick" in football, or to run a sewing machine. The movements of the eye, hand, and foot are under the control of the will, but there are many activities of the body that proceed without our notice and without any effort of the will. Examples of these are the beating of the heart, the movements of the ribs and diaphragm in respiration, the secretion of saliva, gastric juice, and bile when they are needed. Our food is under our control until the muscles of the throat have contracted in swallowing; after that it is in the control of involuntary muscles. How does each organ of the body know when to perform its function, how much effort to put forth, and when to stop? The answer is that the different organs are in communication with one another, like the stations of a telegraph system, or the houses on a telephone line. When there is a need for the performing of a function, the organ concerned receives notice of the need, and sets about doing its par

ticular work. When the demand is over, the organ receives notice, and stops its work. This regulation of the body by communication between its parts is the work of the nervous system.

The nervous system is studied in two divisions:

(1) The central nervous system, consisting of the brain and spinal cord, and the nerves that start from these structures;

(2) The sympathetic nervous system, which puts the internal organs into communication with one another and with the central system.

399. Nerve Cells and Their Structure. The parts of the nervous system are made up of nerve tissue, just as muscles are made up of muscle tissue. The unit of nerve tissue is the nerve cell, or neuron (Fig. 293). This con

sists of two parts, the cell body, or cell proper, and extensions of the cell body. The cell body looks much like other cells, except that it has a grayish color. The extensions of the cell body are of two sorts. One of them is the long, slender nerve fiber, or axon. Some cells have one of these; others have two. Cells that have one axon have also shorter extensións, or dendrites. extensións, or dendrites. Dendrites