*Chambers and "Humors" of the Eyeball.*—The crystalline lens together with the suspensory ligament and the ciliary processes form a partition across the eyeball. This divides the eye space into two separate compartments, which are filled with the so-called "humors" of the eye. The front cavity of the eyeball, which is again divided in part by the iris, is filled with the aqueous humor. This is a clear, lymph-like liquid which contains an occasional white corpuscle. It has a feeble motion and is slowly added to and withdrawn from the eye. It is supplied mainly by the blood vessels in the ciliary processes and finds a place of exit through a small lymph duct at the edge of the cornea (Fig. 159).

The back portion of the eyeball is filled with a soft, transparent, jelly-like substance, called the vitreous humor. It is in contact with the surface of the retina at the back and with the attachments of the lens in front, being surrounded by a thin covering of its own, called the hyaloid membrane. The aqueous and vitreous humors aid in keeping the eyeball in shape and also in focusing.

*How we see Objects.*—To see an object at least four things must happen:

1. Light must pass from the object into the eye. Objects cannot be seen where there is no light or where, for some reason, it is kept from entering the eye.

2. The light from the object must be focused (made to form an image) on the retina. In forming the image, an area of the retina is stimulated which corresponds to the form of the object.

3. Impulses must pass from the retina to the brain, stimulating it to produce the sensations.

4. The sensations must be so interpreted by the mind as to give an impression of the object.

*Focusing Power of the Eyeball.*—The eyeball is essentially a device for focusing light. All of its transparent portions are directly concerned in this work, and the portions that are not transparent serve to protect and operate these parts and hold them in place. Of chief importance are the crystalline lens and the cornea. Both of these are lenses. The cornea with its inclosed liquid is a plano-convex lens, while the crystalline lens is double convex.(123) Because of the great difference in density between the air on the outside and the aqueous humor within, the cornea is the more powerful of the two. The crystalline lens, however, performs a special work in focusing which is of great importance. The iris also aids in focusing since it, through the pupil, regulates the amount of light entering the back chamber of the eyeball and causes it to fall in the center of the crystalline lens, the part which focuses most accurately.

[Fig. 161]

Fig. 161—*Diagram showing changes in shape of crystalline lens* to adapt it to near and distant vision.

*Accommodation.*—A difficulty in focusing arises from the fact that the degree of divergence of the light waves entering the eye from different objects, varies according to their distance. Since the waves from any given point on an object pass out in straight lines in all directions, the waves that enter the eye from distant objects are at a different angle from those that enter from near objects. In reality waves from distant objects are practically parallel, while those from very near objects diverge to a considerable degree. To adjust the eye to different distances requires some change in the focusing parts that corresponds to the differences in the divergence of the light. This change, called accommodation, occurs in the crystalline lens.(124) In the process of accommodation, changes occur in the shape of the crystalline lens, as follows:

1. In looking from a distant to a near object, the lens becomes more convex, i.e., rounder and thicker (Fig. 161). This change is necessary because the greater divergence of the light from the near objects requires a greater converging power on the part of the lens.(125)

2. In looking from near to distant objects, the lens becomes flatter and thinner (Fig. 161). This change is necessary because the less divergent waves from the distant objects require less converging power on the part of the lens.

The method employed in changing the shape of the lens is difficult to determine and different theories have been advanced to account for it. The following, proposed by Helmholtz, is the theory most generally accepted:

The lens is held in place back of the pupil by the suspensory ligament. This is attached at its inner margin to the membranous capsule, and at its outer margin to the sides of the eyeball, and entirely surrounds the lens. It is drawn perfectly tight so that the sides of the eyeball exert a continuous tension, or pull, on the membranous capsule, which, in its turn, exerts pressure on the sides of the lens, tending to flatten it. This arrangement brings the elastic force of the eyeball into opposition to the elastic force of the lens. The ciliary muscle plays between these opposing forces in the following manner:

To thicken the lens, the ciliary muscle contracts, pulling forward the suspensory ligament and releasing its tension on the membranous capsule. This enables the lens to thicken on account of its own elastic force. To flatten the lens, the ciliary muscle relaxes, the elastic force of the eyeball resumes its tension on the suspensory ligament, and the membranous capsule resumes its pressure on the sides of the lens. This pressure, overcoming the elastic force of the lens, flattens it.

*Movements of the Eyeballs.*—In order that the light may enter the eyeballs to the best advantage, they must be moved in various directions. These movements are brought about through the action of six small muscles attached to each eyeball. Four of these, named, from their positions, the superior, inferior, internal, and external recti muscles, are attached at one end to the sides of the eyeball and at the other end to the back of the orbit (Fig. 162). These, in the order named, turn the eyes upward, downward, inward, and outward. The other two, the superior and inferior oblique muscles, aid in certain movements of the recti muscles and, in addition, serve to rotate the eyes slightly. The movements of the eyeballs are similar to those of ball and socket joints.

[Fig. 162]

Fig. 162—*Exterior muscles of eyeball.*

*Binocular Vision.*—In addition to directing the eyeballs so that light may enter them to the best advantage from different objects, the muscles also enable two eyes to be used as one. Whenever the eyes are directed toward the same object, an image of this object is formed on the retina of each. Double vision is prevented only by having the images fall on corresponding places in the two eyes. This is accomplished by the muscles. In each act of seeing, it becomes the task of the superior and inferior recti muscles to keep the eyes in the same plane, and of the external and internal recti muscles to give just the right amount of convergence. If slight pressure is exerted against one of the eyes, the action of the muscles is interfered with and, as a consequence, one sees double. The advantages of two eyes over one in seeing lie in the greater distinctness and broader range of vision and in the greater correctness of judgments of distance.

*Visual Sensations.*—The visual sensations include those of color and those of a general sensibility to light. Proof of the existence of these types of sensation is found in color blindness, a defect which renders the individual unable to distinguish certain colors when he is still able to see objects. Color sensations are the results of light waves of different lengths acting on the retina. While the method by which waves of one length produce one kind of sensation and those of another length a different sensation is not understood, the cones appear to be the portions of the retina acted on to produce the color. On the other hand, the rods are sensitive to all wave lengths and give general sensibility to light.

*Visual Perceptions.*—"Seeing" is very largely the mental interpretation of the primary sensations and the conditions under which they occur. For example, our ability to see objects in their natural positions when their images are inverted on the retina is explained by the fact that we are not conscious of the retinal image, but of the mind's interpretation of it through experience. Experience has also taught us to locate objects in the direction toward which it is necessary to turn the eyes in order to see them. In other words, we see objects in the direction from which the light enters the eyes. That the object is not always in that direction is shown by the image in the mirror. The apparent size and form of objects are inferences, and they are based in part upon the size and form of the area of the retina stimulated. We judge of distance by the effort required to converge the eyes upon the objects, by the amount of divergence of the waves entering the pupil, and also by the apparent size of the object.

*The Lachrymal Apparatus.*—Seeing requires that the light penetrate to the retina. For this reason all the structures in front of the retina are transparent. One of these structures, the cornea, on account of its exposure to the air, is liable to become dry, like the skin, and to lose its transparency. To preserve the transparency of the cornea, and also to lubricate the eyelids and aid in the removal of foreign bodies, a secretion, called tears, is constantly supplied.

[Fig. 163]

Fig. 163—*Diagram of irrigating system of the eye.* After wetting the eyeball the tears may also moisten the air entering the lungs.

The lachrymal, or tear, glands are situated at the upper and outer margins of the orbits. They have the general structure of the salivary glands and discharge their liquid by small ducts beneath the upper lids. From here the tears spread over the surfaces of the eyeballs and find their way in each eye to two small canals whose openings may be seen on the edges of the lids near the inner corner (Fig. 163). These canals unite to form the nasal duct, which conveys the tears to the nasal cavity on the same side of the nose. When by evaporation the eyeball becomes too dry, the lids close reflexively and spread a fresh layer of tears over the surface. Any excess is passed into the nostrils, where it aids in moistening the air entering the lungs.



HYGIENE OF THE EYE

*Defects in Focusing.*—The delicacy and complexity of the sense organs of sight render them liable to a number of imperfections, or defects, the most frequent and important being those of focusing. Such defects not only result in the imperfect vision of objects, but they throw an extra strain upon the nervous system and may render the process of seeing exceedingly painful.

A normal eye is able, when relaxed, to focus light accurately from objects which are twenty feet or more away and to accommodate itself to objects as near as five inches. An eye is said to be myopic, or short-sighted, when it is unable to focus light waves from distant objects, but can only distinguish the objects which are near at hand. In such an eye the ball is too long for the converging power of the lenses, and the image is formed in front of the retina (C, Fig. 164).

[Fig. 164]

Fig. 164—*Diagrams illustrating long-sightedness and short-sightedness*, and method of remedying these defects by lenses. A. Normal eye. B. Long-sighted eye. C. Short-sighted eye.

A long-sighted, or hypermetropic, eye is one which can focus light from distant objects, but not from near objects. In such an eye the ball is too short for the converging power of the lenses and the image tends to form back of the retina (B, Fig. 164). These defects in focusing are remedied by wearing glasses with lenses so shaped as to counteract them. Short-sightedness is corrected by concave lenses and long-sightedness by convex lenses, as shown in diagrams above.

Astigmatism is another defect in the focusing power of the eye. In astigmatism the parts of the eye fail to form the image in the same plane, so that all portions of the object do not appear equally distinct. Certain parts of it are indistinct, or blurred. The cause is found in some difference in curvature of the surfaces of the cornea or crystalline lens. It is corrected by lenses so ground as to correct the particular defects present in a given eye.

Whenever defects in focusing are present, particularly in astigmatism, extra work is thrown on the ciliary muscle as well as the muscles that move the eyeballs. The result is frequently to induce a condition, known as muscle weakness, which renders it difficult to use the eyes. Even after the defect in focusing has been remedied, the muscles recover slowly and must be used with care. For this reason glasses should be fitted by a competent oculist(126) as soon as a defect is known to exist. When one is unduly nervous, or suffers from headache, the eyes should be examined for defects in focusing (page 326).

*Eye Strain and Disease.*—The extra work thrown upon the nervous system through seeing with defective eyes, especially in reading and other close work, is now recognized as an important cause of disease. Through the tax made upon the nervous system by the eyes, there may be left an insufficient amount of nervous energy for the proper running of the vital processes. As a result there is a decline of the health. Ample proof that eye strain interferes with the vital processes and causes ill health, is found in the improvements that result when, by means of glasses, this is relieved.

*The Eyes of School Children.*—School children often suffer from defects of vision which render close work burdensome, and cause headache, general nervousness, and disease. Furthermore, the visual defects may be unknown both to themselves and to their parents. Pupils showing indications of eye-strain should be examined by an oculist, and fitted with glasses should defects be discovered.(127) The precaution, adopted by many schools, of having the eyes of all children examined by a competent physician employed for the purpose, is most excellent and worthy of imitation.

*Reading Glasses.*—Many people whose eyes are weak, because slightly defective, find great relief in the use of special glasses for reading and other close work. By using such glasses they may postpone the time when they are compelled to wear glasses constantly. It is in the close work that the extra strain comes upon the eyes, and if this is relieved, one can much better withstand the work of distant vision. The reading glasses should be fitted by a competent oculist, and used only for the purpose for which they are intended.

*General Precautions in the Use of the Eyes.*—If proper care is exercised in the use of the eyes, many of their common ailments and defects may be avoided. Any one, whether his eyes are weak or strong, will do well to observe the following precautions:

1. Never read in light that is very intense or very dim. 2. When the eyes hurt from reading, stop using them. 3. Never hold a book so that the smooth page reflects light into the eyes. The best way is to sit or stand so that the light passes over the shoulder to the book. 4. Never study by a lamp that is not shaded. 5. Practice cleanliness in the care of the eyes. Avoid rubbing the eyes with the fingers unless sure the fingers are clean.

If the eyes are weak, use them less and avoid, if possible, reading by artificial light. Weak eyes are sometimes benefited by bathing them in warm water, or with water containing enough salt to make them smart slightly. Boracic acid dissolved in water (40 grains to 4 ounces of distilled water) is also highly recommended as a wash for weak eyes.

[Fig. 165]

Fig. 165—*Method of procedure in lifting the eyelid* (Pyle).

*Removal of Foreign Bodies from the Eyes.*—Foreign bodies embedded in the eyeball should be removed by the oculist or physician. Small particles of dust or cinder may be removed without the aid of the physician, by exercising proper care. First let the tears, if possible, wash the offending substance to the corner of the eye, or edge of the lid, where it can be removed with a soft cloth. If it sticks to the ball or the under surface of the lid, it will be necessary to find where it is located, and then dislodge it from its position. Begin by examining the lower lid. Pull it down sufficiently to expose the inner surface, and, if the foreign substance be there, wipe it off with the hem of a clean handkerchief. If it is not under the lower lid, it will be necessary to fold back the upper lid. "The patient is told to look down, the edge of the lid and the lashes are seized with the forefinger and thumb of the right hand (Fig. 165), and the lid is drawn at first downward and forward away from the globe; then upward and backward over the point of the thumb or forefinger of the left hand, which is held stationary on the lid, and acts as a fulcrum."(128) The foreign body is now removed in the same manner as from the lower lid. A large lens may be used to good advantage in finding the irritating substance.

*Strong Chemicals in the Eyes.*—Students in the laboratory frequently, through accident, get strong chemicals, as acids and bases, in the eyes. The first thing to do in such cases is quickly and thoroughly to flood the eyes with water. Any of the chemical which remains may then be counteracted by the proper reagent, care being taken to use a very dilute solution. To counteract an acid, use sodium bicarbonate (cooking soda), and for bases use a very dilute solution of acetic acid (vinegar). To guard against getting the counteractive agent too strong for the inflamed eye, it should first be tried on an eye that has not been injured.

*Summary.*—The nervous impulses that cause the sensation of sight are started by light waves falling upon a sensitized nervous surface, called the retina. By means of refractive agents, forming a part of the eyeball in front of the retina, light from different objects is focused and made to form images of the objects upon the surface. In this way the light is made to stimulate a portion of the retina corresponding to the form of the object. This, the image method of stimulation, enables the mind to recognize objects and to locate them in their various positions. While the greater portion of the eyeball is concerned in the focusing of light, the crystalline lens, operated by the ciliary muscle, serves as the special instrument of accommodation. Muscles attached to the eyeballs turn them in different directions, and so adjust them with reference to each other that double vision is avoided.

*Exercises.*—1. Under what conditions are light waves reflected, refracted, and absorbed?

2. Why does the body not need a light-producing apparatus, corresponding to the larynx in the production of sound?

3. How is the light from a candle made to form an image?

4. What different things must happen in order that one may see an object?

5. Make a sectional drawing of the eyeball, locating and naming all the parts.

6. Of what parts are the outer, middle, and inner coats of the eyeball made up?

7. What portions of the eyeball reflect light? What absorb light? What transmit light? What refract light?

8. Show how the iris, the crystalline lens, the retina, the ciliary muscle, and the cornea aid in seeing.

9. Trace a wave of light from a visible object to the retina.

10. Why does not the inverted image on the retina cause us to see objects upside down?

11. What change occurs in the shape of the crystalline lens when we look from distant to near objects? From near to distant objects? Why are these changes necessary? How are they brought about?

12. How does the method of adjustment, or accommodation, of the eyeball differ from that of a telescope or a photographer's camera?

13. With two eyes how are we kept from seeing double?

14. What different purposes are served by the tears. Trace them from the lachrymal glands to the nostrils.

15. Show how the proper lenses remedy short- and long-sightedness.

16. Describe the conjunctiva and give its functions. Why should it be so sensitive?

17. How may eye strain cause disease in parts of the body remote from the eyes?

18. How does "image stimulation" differ from light stimulation in general?



PRACTICAL WORK

*To illustrate Simple Properties of Light.*—1. Heat an iron or platinum wire in a clear gas flame. Observe that when a high temperature is reached it gives out light or becomes luminous.

2. Cover one hand with a white and the other with a black piece of cloth, and hold both for a short time in the direct rays of the sun. Note and account for the difference in temperature which is felt.

3. Stand a book or a block of wood by the side of an empty pan in the sunlight, so that the end of the shadow falls on the bottom of the pan. Mark the place where the shadow terminates and fill the pan with water. Account for the shadow's becoming shorter.

4. Place a coin in the center of an empty pan and let the members of the class stand where the coin is barely out of sight over the edges of the pan. Fill the pan with water and account for the coin's coming into view. Show by a drawing how light, in passing from the water into the air, is so bent as to enter the eye.

5. With a convex lens, in a darkened room, focus the light from a candle flame so that it falls on a white screen and forms an image of the candle. Observe that the image is inverted. In a well-lighted room focus the light from a window upon a white screen. Show that, as the distance from the window to the screen is changed, the position of the lens must also be changed. (Accommodation.)

6. Hold a piece of cardboard, about eight inches square and having a smooth, round hole an eighth of an inch in diameter in the center, in front of a lighted candle in a darkened room. Back of the opening place a muslin or paper screen (Fig. 157). Observe that a dim image is formed. Account for the fact that it is inverted. Hold a lens between the cardboard and the screen so that the light passes through it also. The image should now appear smaller and more distinct.

[Fig. 166]

Fig. 166—*Diagram* for proving presence of the blind spot.

*To prove the Presence of the Blind Spot.*—Close the left eye and with the right gaze steadily at the spot on the left side of this page (Fig. 166). Then starting with the book a foot or more from the face, move it slowly toward the eye. A place will be found where the spot on the right entirely disappears. On bringing it nearer, however, it is again seen. As the book is moved forward or backward, the position of the image of this spot changes on the retina. When the spot cannot be seen, it is because the image falls on the blind spot.

*Dissection of the Eyeball.*—Procure from the butcher two or three eyeballs obtained from cattle. After separating the fat, connective tissue, and muscle, place them in a shallow vessel and cover with water. Insert the blade of a pair of sharp scissors at the junction of the sclerotic rotic coat with the cornea and cut from this point nearly around the entire circumference of the eyeball, passing near the optic nerve. Spread open in the water and identify the different parts from the description in the text. Open the second eyeball in water by cutting away the cornea. Examine the parts in front of the lens.

[Fig. 167]

Fig. 167—*Model* for demonstrating the eyeball.

*To illustrate Accommodation.*—Paste together the ends of a strip of stiff writing paper (two by five inches) making a ring a little less than three inches in diameter. This is to represent the crystalline lens. Now paste a piece of thin paper (two by seven inches) upon a second strip of the same size, leaving an open place in the middle for the insertion of the paper lens. A flexible piece of cardboard (three by twelve inches) is now bent into the form of a half circle and to its ends are fastened the strips of paper containing the ring. Make a small hole in each of the four corners of the bent cardboard. Through these holes pass two loops of thread, or fine string, in opposite directions, letting the ends hang loose from the cardboard.

When everything is in position, the tension from the cardboard flattens the paper lens, while pulling the strings releases this tension and permits the lens to become more rounded. With this simple device the changes in the curvature of the lens for near and distant vision are easily shown.



CHAPTER XXIII - THE GENERAL PROBLEM OF KEEPING WELL

"To cure was the voice of the Past: to prevent is the divine whispering of To-day."

As stated in the introduction to our study, the fundamental law of hygiene is the law of harmony: Habits of living must harmonize with the plan of the body. Having acquainted ourselves with the plan of the body, we may now review briefly those conditions that help or hinder its various activities. The hygiene already presented in connection with the study of the various organs may be condensed into general rules, or laws, as follows:

1. Of exercise: Exercise daily the important groups of muscles.

2. Of form: Preserve the natural form of the body.

3. Of energy: Observe regular periods of rest and exercise and avoid exhaustion.

4. Of nutriment: Eat moderately of a well-cooked and well-balanced diet and drink freely of pure water.

5. Of respiration: Breathe freely and deeply of pure air and spend a part of each day out of doors.

6. Of nervous poise: Suppress wasteful and useless forms of nervous activity, avoid nervous strain, and practice cheerfulness.

7. Of cleanliness: Keep the body and its immediate surroundings clean.

8. Of restraint: Abstain from the unnecessary use of drugs as well as from the practice of any form of activity known to be harmful to the body.

9. Of elimination: Observe all the conditions that favor the regular discharge of waste materials from the body.

Obedience to these laws is of vast importance in the proper management of the body. They should, indeed, be so thoroughly impressed upon the mind as to become fixed habits. There are, however, other conditions that relate to this problem, and it is to these that we now turn. These conditions have reference more specifically to

*The Prevention of Disease.*—While the average length of life is not far from thirty-five years, the length of time which the average individual is capable of living is, according to some of the lowest estimates, not less than seventy years. This difference is due to disease. People do not, as a rule, die on account of the wearing out of the body as seen in extreme old age, but on account of the various ills to which flesh is heir. It is true that many people meet death by accident and not a few are killed in wars, but these numbers are small in comparison with those that die of bodily disorders. The prevention of disease is the greatest of all human problems. Though the fighting of disease is left largely to the physician, much is to be gained through a more general knowledge of its causes and the methods of its prevention.

*Causes of Disease.*—Disease, which is some derangement of the vital functions, may be due to a variety of causes. Some of these causes, such as hereditary defects, are remote and beyond the control of the individual. Others are the result of negligence in the observance of well-recognized hygienic laws. Others still are of the nature of influences, such as climate, the house in which one lives, or one's method of gaining a livelihood, that produce changes in the body, imperceptible at the time, but, in the long run, laying the foundations of disease. And last, and most potent, are the minute living organisms, called microbes or germs, that find their way into the body. Although there are two general kinds of germs, known as bacteria (one-celled plants) and protozoa (one-celled animals), most of our germ diseases are caused by bacteria.

*Effects of Germs.*—While there are many kinds of germs that have no ill effect upon the body and others that are thought to aid it in its work, there are many well-known varieties that produce effects decidedly harmful. They gain an entrance through the lungs, food canal, or skin, and, living upon the fluids and tissues, multiply with great rapidity until they permeate the entire body. Not only do they destroy the protoplasm, but they form waste products, called toxins, which act as poisons. Diseases caused by germs are known as infectious, or contagious, diseases.(129) The list is a long one and includes smallpox, measles, diphtheria, scarlet fever, typhoid fever, tuberculosis, la grippe, malaria, yellow fever, and others of common occurrence. In addition to the diseases that are well pronounced, it is probable that germs are responsible also for certain bodily ailments of a milder character.(130)

*Avoidance of Germ Diseases.*—The problem of preventing diseases caused by germs is an exceedingly difficult one and no solution for all diseases has yet been found. One's chances of avoiding such diseases, however, may be greatly enhanced:

1. By strengthening the body through hygienic living so that it offers greater resistance to the invasions of germs.

2. By living as far as possible under conditions that are unfavorable to germ life.

3. By understanding the agencies through which disease germs are spread from person to person.

*Conditions Favorable and Unfavorable for Germs.*—Conditions favorable for germ life are supplied by animal and vegetable matter, moisture, and a moderate degree of warmth. Hence disease germs may be kept alive in damp cellars and places of filth. Even living rooms that are poorly lighted or ventilated may harbor them. Water may, if it contain a small per cent of organic matter, support such dangerous germs as those of typhoid fever. Fresh air, sunlight, dryness, cleanliness, and a high temperature, on the other hand, are destructive of germs. The germs in impure water, as already noted (page 165), are destroyed by boiling.

*How Germs are Spread.*—Some of the more common methods by which the germs of disease are spread, and by so doing find new victims, are as follows:

1. By Means of Foods.—Foods, on account of the locality in which they are produced or the method of gathering or of handling-them, may become contaminated with germs, which are then transported with the foods to the consumer.

2. By Means of Dust.—Material containing germs, e.g., discharges from the throat and lungs, will on drying form dust. This is lifted with other fine particles by the air and may be carried quite a distance. The dust from public halls and other places where people congregate is the kind most likely to contain disease germs. Dust should be breathed as little as possible and only through the nostrils. Where one is compelled, as in sweeping, to breathe dust-laden air for some time, he should inhale through a moistened sponge, or cloth, tied in front of the nostrils.

3. By Means of Domestic Pets and Different Kinds of Household Vermin.—Germs sticking to the bodies of small animals are carried about and may be easily communicated to people. By this means, rats, mice, bedbugs, etc., where such exist, are frequently the means of spreading disease; and particularly dangerous, on this account, is the common house fly. Feeding as it does on filth of all kinds, it is easy for it to transfer the bacteria that may stick to its body to the food which is supplied to the table. The proper screening of houses and the destruction of material in which flies may develop, such as the refuse from stables, are necessary precautions.

Germs are spread also by the clothing of people, by railroad and steamship lines, by the mails, and by the natural elements. In fact, any kind of carrier, in or upon which germs can live, may serve as a means of spreading those of certain kinds.

*Public Sanitation.*—The general conditions under which germs may thrive and some of the means by which they are scattered, emphasize the practical value of measures which have for their purpose the making of one's surroundings more wholesome and hygienic. Such measures may be directed both toward one's immediate surroundings—the home—and toward the neighborhood, town, or city in which one lives. The hygienic conditions of primary importance in every city or town are as follows:

1. An adequate public supply of pure water.

2. An efficient system of underground pipes for the removal of sewage.

3. An efficient system for removing from the streets and alleys everything of the nature of waste.

4. Prevention, by enforcement of ordinances, of spitting upon sidewalks and the floors of public halls and conveyances.

5. A hospital or sanitarium in which people can be cared for when sick with infectious diseases.

In the larger cities other hygienic measures demand attention, such as provisions for parks and playgrounds, the proper housing of the poor of the city, and the suppression of the smoke and dust nuisances. Crowded together as people are in the cities, the welfare of each individual depends in a large measure upon the welfare of all. Hence the problems of public sanitation are matters in which all are vitally concerned.

*Sanitary Conditions of the Home.*—The home, being the feeding and resting place for the entire family, is the most important factor in one's physical, as well as moral, environment. For this reason there is no place where careful attention to hygienic requirements will yield better results. Much of the danger from germs may be prevented by instituting and maintaining proper sanitary conditions in and about the home.

One of the first requisites of the home is a suitable location for the house. The house should be built upon ground that is well drained, and if natural drainage be lacking, artificial drainage must be supplied. It should not be situated nearer than a quarter of a mile to any marsh or swamp and, if so near as that, it ought to be on the side from which the wind usually blows. A stone foundation should be provided, and at least eighteen inches of ventilated air space should be left between the ground and the floor. Ample provisions must be made for pure air and sunlight in all the rooms. The cellar, if one is desired, needs to be constructed with special care. It should be perfectly dry and provided with windows for light and ventilation. Adequate means must also be provided, by sewage pipes and other methods, for the disposal of all waste. Where drainage pipes are provided, care must be taken to prevent the entrance of sewer gas into the house and also the passage of material from these pipes into the water supply. The placing and connecting of sewer pipes should, of course, be under the direction of a plumber.

*The Water Supply.*—Since water readily takes up and holds the impurities with which it comes in contact, it should be exposed as little as possible in the process of collecting. Where cistern water is used, care must be taken to prevent filth from the roof (Fig. 168), water pipes, or soil from getting into the reservoir. Water should be collected from the roof only after it has rained long enough for the roof and pipes to have been thoroughly cleaned. The cistern should have no leaks (Fig. 169), and the top should be tightly closed to prevent the entrance of small animals and rubbish.

[Fig. 168]

Fig. 168—*Contamination of cistern water* by birds nesting in the gutter trough.

Shallow wells are to be condemned, as a rule, because of the likelihood of surface drainage (Fig. 169), and water from springs should, for the same reason, be used with caution. Deep wells that are kept clean usually may be relied on to furnish water free from organic impurities, but such water often holds in solution so much of mineral impurities as to render it unfit for drinking. The presence in water of any considerable quantity of the compounds of iron or calcium makes it objectionable for regular use.

[Fig. 169]

Fig. 169—*Sources of contamination of cistern and well water.* Illustration shows liability of contamination from surface drainage and from entrance of filth at top.

*Hygienic Housekeeping.*—However carefully a house has been constructed from a sanitary standpoint, the constant care of an intelligent housekeeper is required to keep it a healthful place in which to live. Daily cleaning and airing of all living rooms are necessary, while such places as the kitchen, the cellar, and the closets need extra thoughtfulness and, at times, hard work. Moreover, the problem is not all indoors. The immediate premises must be kept clean and sightly, and all decaying vegetable and animal matter should be removed. Home sanitation consists, not of one, but of many, problems, all more or less complex. None of these can be slighted or turned over to a novice.

*Destruction of Infectious Material.*—At times the housekeeping has to be directed especially toward hygienic requirements, such an occasion being the sickness of one of the inmates with some contagious disease. Unless special precautions are taken, the disease will spread to other members of the household and may reach people in the neighborhood. Not only must great care be exercised that nothing used in connection with the sick shall serve as a carrier of disease, but germs passing from the patient should, as far as possible, be actually destroyed. All discharges from the body likely to contain bacteria, should be burned or treated with disinfectants and buried deeply at a remote distance from the water supply to the house.

After recovery all clothing, bedding, and furniture used in connection with the sick should be disinfected or burned. The room also in which the sick was cared for should be thoroughly disinfected and cleaned; in some instances the woodwork ought to be repainted and the walls repapered or calcimined. The purpose is, of course, to destroy all germs and prevent, by this means, a recurrence of the disease.

*Fumigation.*—To destroy germs in the air or adhering to the walls of rooms, furniture, clothing, etc., fumigation is employed. This is accomplished by saturating the air of rooms with some vapor or gas which will destroy the germs. Fumigation is quite generally employed in the general cleaning after the patient leaves his room. This, to be effective, must be thorough. Formaldehyde is considered the best disinfectant for this purpose, and it should be evaporated with heat in the proportion of one half pint of the 40 per cent solution to 1000 cu. ft. of space. Since formaldehyde is inflammable and easily boils over, it has to be evaporated with care. It should be boiled in a tall vessel (a tin or copper vessel which holds about four times the quantity to be evaporated) over a quick fire, the room being tightly closed (openings around windows and doors plugged with cotton or cloth). After three or four hours the room may be opened and thoroughly aired. Since formaldehyde is most disagreeable to breathe, one should not attempt to occupy the room until it is free from the gas. This will require a day or more of thorough ventilation.

*Facts Relating to the Spread of Certain Diseases.*—The problem of preventing disease in general often resolves itself into the problem of preventing the spread of some particular disease. It is then of vital importance to know the special method by which the germs of this disease leave the body of the patient and are conveyed to the bodies of others. Some of these methods are novel in the extreme, and are not at all in accord with prevailing notions. Particularly is this true of that disease known as

*Malaria, or Malarial Fever.*—This disease, so common in warm climates and also prevalent to a large extent in the temperate zones, is due to animal germs (protozoa), which attack and destroy the red corpuscles of the blood. These germs, it is found, pass from malarial patients to others through the agency of a variety of mosquitoes known as Anopheles. In sucking the blood of a malarial patient, the mosquito first infects her own body.(131) In the body of the mosquito the germs undergo an essential stage of their development, after which they are injected beneath the skin of whomsoever the mosquito feeds upon. For the spreading of malaria, then, two conditions are necessary: first, there must be people who have the disease; and second, there must be in the neighborhood the special variety of mosquito that spreads the disease. If either condition be lacking, the disease is not spread. The malarial mosquito (Anopheles) may be distinguished from the harmless variety (Culex) by the position which it assumes in resting, as shown in Fig. 170.

[Fig. 170]

Fig. 170—*Mosquitoes* in resting position. (From Howard's Mosquitoes.) On left the malarial mosquito (Anopheles); on the right the harmless mosquito (Culex).

*Remedies against Mosquitoes.*—The natural method of preventing the spread of malaria is, of course, the destruction of mosquitoes. This is accomplished by draining pools of water where they are likely to breed, and by covering pools of water that cannot be drained with crude petroleum or kerosene. The kerosene, by destroying the larvae, prevents the development of the young. In communities where such measures have been diligently carried out, the mosquito pest has been practically eliminated. Other methods are also under investigation, such as the stocking of shallow bodies of water with varieties of fish that feed upon the mosquito larvae.

[Fig. 171]

Fig. 171—*Stegomyia*, the yellow-fever mosquito (after Howard).

*Yellow Fever.*—This scourge of the tropics is, like malaria, caused by animal germs. It is also propagated in the same manner as malaria, but by a different variety of mosquito (Stegomyia, Fig. 171). The stamping out of yellow fever in Havana, the Panama Canal Zone, and other places, through the destruction of this variety of mosquito, affords ample proof of the correctness of the "mosquito theory."

[Fig. 172]

Fig. 172—*Consumption germs* from the spit of one having the disease. Highly magnified and stained. (Huber's Consumption and Civilization.)

*Consumption*, or tuberculosis of the lungs, spoken of as the "white plague," was among the first diseases shown to be due to bacteria. Consumption is now recognized as an infectious disease, though not so readily communicated as some other diseases. Several methods are recognized by which the germs are passed from the sick to the well, the most important being as follows:

1. By personal contact of the sick with the well, especially in kissing.

2. By the sputum, or spit, which, if allowed to dry, is blown about as dust and breathed into the lungs(132) (Fig. 172).

3. By means of objects (drinking cups, tableware, etc.) that have been handled by consumptives.

4. By infectious material associated with houses or rooms in which consumptives have lived.

These methods of spreading consumption suggest the necessity for the greatest care, on the part of both the patient and those having him in charge.(133) The material coughed up from the lungs and throat should be collected on cloths or paper handkerchiefs and afterwards burned. The house where a consumptive has lived should be disinfected, repapered or calcimined, and thoroughly cleaned before it is again occupied. The inside woodwork should also be repainted. The approaches to the house where the patient may have expectorated should be disinfected and cleaned. Since the germs are able to live in the soil, fresh lime or wood ashes should be spread around the doorsteps and along the walks.

*Typhoid Fever*, one of our most dangerous diseases, is caused by germs (bacteria) that enter the body through the food canal. They attack certain glands in the walls of the small intestine, where they produce toxins that pass with the germs to all parts of the body. Typhoid fever germs spread from those having the disease to others, chiefly through the discharges from the bowels and the kidneys. The germs contained in these, if not destroyed by disinfectants, find their way into the soil, or into sewage, where they may be picked up by water and widely distributed. Finding suitable places, such as those containing decaying material, the germs may rapidly increase in number, and from these sources find their way into the bodies of new victims. They are likely, on account of manures, to get on vegetables; on account of uncleanly methods of milking, to get into the milk supply; and from sewerage outlets, to get into the oysters that grow in bays and harbors near seaboard cities; but they are most frequently introduced into the body through the drinking of impure water.

*Diphtheria*, also known as "membranous croup," is caused by germs that attack the membranes of the throat. This most dangerous of children's diseases is spread chiefly by discharges from the mouth and throat. These should be collected on cloths and burned, or rendered harmless with disinfectants. The disease may be spread also by objects brought into contact with the mouth, such as cups, toys, pencils, etc. Children are known to have diphtheria germs in the mouth for some time after recovering from the disease, and should, for this reason, be kept away from other children until pronounced safe by the physician.

The antitoxin method of treating diphtheria has robbed this disease of much of its terror, yet it not infrequently happens that the physician is called too late to administer this remedy to the best advantage. Since certain cases of diphtheria are likely to be mistaken for croup, the parent frequently does not realize the serious condition of the child. A croupy cough that lasts through the day, or a sore throat which shows small white patches, are indications of diphtheria.

*Scarlet Fever, Measles, Chicken Pox, and Smallpox*, on account of the eruptions of the skin which attend them, are classed as eruptive diseases. As the eruptions heal, scales separate from the skin, and these are supposed to be the chief means of spreading the germs. Attention must be given to the destruction of these scales by burning or thoroughly disinfecting all objects, such as clothing, bedding, etc., that may serve as carriers of them. Those having eruptive diseases should be confined to their rooms as long as the scales continue to separate from the body.

*Vaccination.*—The method of preventing smallpox known as vaccination, which has been practiced since its discovery in 1796 by Jenner, has always proved effective. In some instances the sore arm causes considerable inconvenience, but this generally results from neglect to cleanse the arm thoroughly before applying the virus, or from contact of the sore with the clothing later. The virus should be applied by a physician and the wound should be protected after the operation. If discomfort is felt when it "takes," medical advice should be sought.

*Isolation*, or quarantining, is a most important method of combating contagious diseases. By removing the sick from the well many outbreaks of disease are quickly checked. Isolation of individual patients, and sometimes of infected neighborhoods, is absolutely necessary; and while this works a hardship to the few, it is frequently the only safeguard of the many. The community, on the other hand, should make ample provision for the care of the afflicted in the way of hospitals, or sanitaria, and if it is deemed necessary to remove people from their homes, they should not be subjected to unnecessary hardship.

Where one is sick from some contagious disease in the home and there is liability of communicating it to the other members of the family, room isolation should be practiced. Infection cannot spread through solid walls, and where the doors, and the cracks around the doors, are kept completely closed and the usual precautions are observed by those attending the patient, the other inmates of the house can be protected from the disease.

*The Physician and His Work.*—In combating disease the services of the physician are a prime necessity. The special knowledge which he has at his command enables the conflict to be carried on according to scientific requirements and vastly increases the chances for recovery. He should be called early and his directions should be carefully followed. Everything, however, must not be left to the physician, for recovery depends as much upon proper nursing and feeding as upon the drugs that are administered. Of great importance is the saving of the energy of the patient, and to accomplish this visitors should, as a rule, be excluded from the sick room.

*Precautions in Recovery from Disease.*—Many diseases, if severe, not only leave the body in a weakened condition, but may, through the toxins which the germs deposit, cause untold harm if the patient leaves his bed or resumes his usual activities too soon. Especially is this true of typhoid fever,(134) diphtheria, scarlet fever, and measles. Rheumatism and affections of the heart, lungs, kidneys, and other bodily organs frequently follow these diseases, as the result of slight exposure or exertion before the body has sufficiently recovered from the effects of the toxins. To guard against such results, certain physicians require their patients to keep their beds for a week, or longer, after apparent recovery from diseases like typhoid fever, diphtheria, and scarlet fever.

*Relation of Vocation to Disease.*—With a few exceptions, the pursuit of one's vocation, or calling in life, does not supply either the quantity or the kind of activity that is most in harmony with the plan of the body. Especially is this true of work that requires most of the time to be spent indoors, or which exercises but a small portion of the body. The effect of such vocations, if not counteracted, is to weaken certain organs, thereby disturbing the functional equilibrium of the body—a result that may be brought about either by the overwork of particular organs or by lack of exercise of others. Herein lies the explanation of the observed fact that people of the same calling in life have similar diseases.

*A Special Problem for the Brain Worker.*—Farthest removed from those forms of activity which harmonize with the plan of the body, and which therefore are most hygienic, is that class of workers known as the professional class, or the "brain workers." This class includes not only the members of the learned professions—law, medicine, and the ministry—but a vast army of business men, engineers, teachers, stenographers, office clerks, etc., a class that is ever increasing as our civilization advances. It is this class in particular that must give attention to those conditions that indirectly, but profoundly, influence the bodily well-being and must seek to obviate if possible such weaknesses as the occupation induces.

*The Remedy* lies in two directions—that of spending sufficient time away from one's work to allow the body to recover its normal condition, and that of counteracting the effect of the work by special exercise or other means. In many cases the first symptoms of weakness indicate a suitable remedy. Thus exhaustion from overwork suggests rest and recreation. The diverting of too much blood from other parts of the body to the brain suggests some form of exercise which will equalize the circulation. If feebleness of the digestive organs is being induced, some natural method of increasing the blood supply to these organs is to be looked for. And effects arising from lack of fresh air and sunlight are counteracted by spending more time out of doors.

*Exercise as a Counteractive Agent.*—In counteracting tendencies to disease and in the maintenance of the functional equilibrium of the body, no agent has yet been discovered of greater importance than physical exercise, when applied systematically and persistently. This may consist of exercises that call into play all the muscles of the body, or which are concentrated upon special parts. When general tonic effects are desired, the exercise should be well distributed; but when counteractive or remedial effects are wanted, it must be applied chiefly to the parts that are weak or that have not been called into action by the regular work. Unfortunately, health is sometimes confused with physical strength and exercise is directed toward the stronger parts of the body with the effect of making them still stronger. Not only is health not to be measured by the pounds that one can lift or by some gymnastic feat that one can perform, but the possession of great muscular power may, if the heart and other vital organs be not proportionally strong, prove a menace to the health. This being true, one having his health primarily in view will use physical exercise, in part at least, as a means of building up organs that are weak. Since the body, like a chain, can be no stronger than its weakest part, this is clearly the logical method of fortifying it against disease.

*Value of Work.*—Although there may exist in one's vocation certain tendencies to disease, it must not be inferred that work in itself is detrimental to health. Health demands activity, and those forms of activity that provide a regular and systematic outlet for one's surplus energy and compel the formation of correct habits of eating, sleeping, and recreating best serve the purpose. Work furnishes activity of this kind and serves also as a safeguard against the unhealthful and immoral habits contracted so often from idleness. Even physical exercise which has for its purpose the reenforcement of the body against disease may frequently consist of useful work without diminishing its hygienic effects.

*The Mental Attitude.*—While a proper thoughtfulness and care for the body is both desirable and necessary, it is also true that over-anxiety about, or an unnatural attention to, the needs of the body reacts unfavorably upon the nervous system. Observance of the laws of health, therefore, should be natural and without special effort—a matter of habit. The attention should never be turned with anxiety upon any organ or process, but the mental attitude should at all times be that of confidence in the power of the body organization to do its work. Fear and morbidity, which are disturbing and paralyzing factors, should be supplanted by courage, cheerfulness, and hopefulness.

Let it be borne in mind that hygienic living requires nothing more than the application of the same intelligence and practical common sense to the care of the body that the skillful mechanic applies to an efficient, but delicate, machine. And, just as in the case of the machine, care of the body keeps its efficiency at the maximum and lengthens the period that it may be used. This end and aim of hygienic living is best attained by cultivating that attitude of mind toward the body that avoids interference in the vital processes and permits the natural appetites, sensations, and desires to indicate very largely the body's needs.

*Attitude toward Habit-forming Drugs.*—Among the different substances introduced into the body, either as foods or as medicines, are a number which have the effect of developing an artificial appetite or craving which leads to their continued use. Since the effect of such substances is usually harmful and since they tend to engraft themselves upon communities as social customs, they present a twofold relation to the general problem of keeping well. The individual may be injured through the personal use which he makes of them, or he may be injured through the effect which they have upon relatives or friends or upon society at large. Since our social environment is a factor in health little less important than our physical environment, the conditions that make for their continuance should be more generally understood.

*How Social Agencies perpetuate the Use of Habit-forming Drugs.*—When the use of some habit-forming drug has risen to the importance of a general custom, a number of conditions arise which tend to continue its use, even though the fact may be quite generally known that the substance does harm. In the first place, those who have formed the habit suffer inconvenience and distress when deprived of its use. In the second place, a number of people will have become interested in the production and sale of the substance, and these will lose financially if it is discontinued. In the third place, those of the rising generation will, from imitation or persuasion, be constantly acquiring the habit before they are sufficiently mature to decide what is best for them. Thus may the use of a substance most harmful, such as the opium of the Chinese, be indefinitely continued—a species of slavery from which the individual finds it hard to escape.

Such is human nature and such are the forces and influences of human society, that the freeing of a people from the bondage of some habit-forming drug cannot be accomplished without strenuous and persistent effort. Education, persuasion, the good example of abstainers, and legal restrictions must be pitted against the forces that make for its continuance. Such a struggle is now in progress in all civilized countries relative to the use of alcoholic beverages.(135)

*How the Use of Alcohol became a Social Custom.*—The general use of alcohol as a beverage may be accounted for by three facts. Alcohol is a habit-forming drug; it has a stimulating effect which many have found agreeable; and being a product of the fermentation of fruit juices and other liquids containing sugar, it is easily obtained. Through the operation of these causes the human family became habituated very early to the use of alcohol. The "wine" of primitive man, however, did little harm as compared with the alcoholic liquors of modern times. It was a weak solution and on account of the crude methods of manufacture and storage could only be produced in limited quantities. Perhaps the worst effect of its early use was the establishment of a general belief in its power to benefit, since this laid the foundation for excess in its use when the developments of a later period made it possible.

During the eleventh century the method of making alcoholic drinks from starch-producing substances, such as wheat, barley, and potatoes, became quite generally known, and also the method of concentrating them by distillation. This knowledge made possible the manufacture of alcoholic drinks in large quantities and in considerable variety. Alcoholic indulgence was now no longer the pastime of the few, but the privilege of all. Its evil effects followed as a matter of course; and as these became more and more apparent, there began the struggle to restrict the consumption of alcohol which has continued with varying success to the present time.

*Counts against Alcohol.*—The statements found in different parts of this book relative to the effects of alcohol upon the body may here be summarized as follows:—

1. Alcohol has an injurious effect upon the white corpuscles of the blood and lessens the power of the body to resist attacks of disease (pages 35, 98).

2. Alcohol injures the heart and the blood vessels (page 56).

3. Alcohol causes diseases of the liver and kidneys and interferes with the discharge of waste through these organs (pages 210, 212).

4. Alcohol interferes seriously with the regulation of the body temperature (page 271).

5. Alcohol is one of the worst enemies to the nervous system (pages 326, 332-334. 336, 337).

6. Through its effect upon the nervous system and through its interference with the production of bodily energy (page 195), alcohol greatly diminishes the efficiency of the individual.

7. The taking of alcohol in amounts that apparently do not harm the tissues is, nevertheless, liable to produce a habit which leads to its use in amounts that are decidedly harmful.

*Alcohol and the Social Environment.*—Our social environment includes the people with whom we are directly or indirectly associated. The presence in any community of those who are immoral, inefficient, or defective, places a burden upon those who are mentally and physically capable and renders them liable to results which are the outgrowth of weakness or viciousness. The fact that alcohol causes pauperism, crime, and general inefficiency, thereby rendering the social environment less conducive to what is best in life, is plainly evident. To realize how alcohol harms the individual through its effects upon society in general, one has only to take into account his dependence upon society for intellectual and moral stimuli, for industrial and economic opportunity, for protection, and for general conditions that make for health and happiness. As we strive to improve our physical environment, so should we also strive for the betterment of social conditions.

*Industrial Use of Alcohol.*—Interesting and instructive in this connection is the fact that alcohol is, after all, a substance capable of rendering great service to humanity. The injury which it causes is the result of its misuse. Though unfit for introduction into the human body, except in the most guarded manner, it is adapted to a great variety of uses outside of the body. A combustible substance which is readily convertible into a gas, it may be substituted for gasoline in the cooking of food, lighting of dwellings, and the running of machinery. As a solvent for gums, resins, essential oils, etc., it is used in the preparation of varnishes, extracts, perfumes, medicines, and numerous other substances of everyday use. Through its chemical interactions, it is used in the manufacture of ether, chloroform, explosives, collodion, celluloid, dyestuffs, and artificial silk. In fact, alcohol is stated by one authority to be, next to water, the most valuable liquid known.(136)

Opposed to an extensive use of alcohol for industrial purposes is the guard which the government must keep over its manufacture on account of its use in beverages. Though alcohol may be profitably manufactured and sold at thirty cents per gallon, the government revenue stamp of $2.08 per gallon practically prohibits its use for many purposes. A step toward a wider application to industrial purposes has been taken by the law permitting the sale of so-called "denatured"(137) alcohol without the tax for revenue. This law has proved beneficial to some extent, though the practical solution of the problem is still remote.

*Nicotine and Social Custom.*—The influences which brought about a general use of tobacco are similar to, though not identical with, those that engrafted alcohol upon society. The drug nicotine is a habit-forming substance and the plant producing it is easily cultivated.(138) Its immediate effect upon the user is generally agreeable, acting as a stimulant to some, but having a soothing effect upon the nerves of others. Moreover, a strong deterring factor in its use is lacking, since its harmful effects are not readily discernible and by many are avoided through moderation in its use.

As with alcohol, tobacco is conveniently used to promote sociability among men, a fact which has much to do with its very general use. If it could be limited to social purposes, it would likely do little harm, but the habit, once started, is continued without reference to sociability—a matter of selfish indulgence. In fact, one effect of tobacco is to cause the user to become less sensitive to the rights of others, this being evidenced by smokers who do not hesitate to make rooms and public halls almost unbearable to those unaccustomed to tobacco.

*Counts against Nicotine.*—The physiological objections to the use of tobacco, as already stated (pages 56, 92, 326, 333, 336), are the following:—

1. The use of tobacco before one reaches maturity stunts the growth. The boy who uses it cannot develop into so strong and capable a man as he would by leaving it alone.

2. Tobacco injures the heart.

3. Tobacco injures the air passages, especially when inhalation is practiced.

4. Tobacco injures the nervous system and by this means interferes in a general way with the bodily processes. For the same reason it interferes with mental and moral development, the cigarette being a chief cause of criminal tendencies in boys.

5. In some cases tobacco injures the vision.

6. The tobacco habit is expensive and is productive of no good results.

*Tobacco and the Rising Generation.*—The problem of limiting the use of tobacco to the point where it would do slight harm, in comparison to what it now does, would be solved if those under twenty years of age could be kept from using it. But few would then acquire the habit, and those who did would not be so seriously injured. In our own country it lies within the province of the home and the school to bring about this result. The fact that parents use tobacco is no reason why the boys should also indulge. The decided difference in effects upon the young and upon the mature makes this point very clear. Laws protecting boys from the evil effects of tobacco, not only cigarettes, but other forms as well, are both just and necessary.

*Social Custom and the Caffeine Habit.*—By suitable processes a white, crystalline solid, easily soluble in water, can be separated from the leaves of tea, and from the berry of the coffee plant. This is the drug caffeine, the substance which gives to tea and coffee their stimulating properties, but not their agreeable flavors. Less injurious, on the whole, than either alcohol or tobacco, caffeine has come into general use in much the same way as these substances. In a sense, however, caffeine is more deceptive than either alcohol or nicotine, because the usual mode of preparing tea and coffee gives them the appearance of real foods. The housewife who would feel condemned in purchasing caffeine put up as a drug somehow feels justified when she extracts it from plant products in the regular preparation of the meal.

*Counts against Caffeine.*—People of vigorous constitutions and of active outdoor habits are injured but slightly, if at all, by either tea or coffee when these are used in moderation. As already stated (pages 56, 167, 326, 329), they do harm when used to excess and, in special cases, in very small amounts, in one of the following ways:—

1. By stimulating the nervous system, thereby causing nervousness and insomnia and interfering with vital organs.

2. By introducing a waste which forms uric acid into the body, thereby throwing an extra burden upon the organs of elimination.

In this connection it may also be stated that there appears to be little, if any, real advantage to the healthy body from the use of either tea or coffee, beyond that of temporary stimulation and the gratification of an appetite artificially acquired. Hence the large sums of money expended for these substances in this country yield no adequate returns.

*Caffeine Restrictions Necessary.*—Though with many the cup of tea or coffee at breakfast does no harm, but gives an added pleasure to the meal, there is no question but that the use of caffeine beverages should be greatly curtailed. Children should not be permitted to drink either tea or coffee. Brain workers and indoor dwellers generally should use these substances very sparingly, and people having a tendency to indigestion, nervousness, constipation, rheumatism, or diseases of the heart, kidneys, or liver frequently find it best to omit them altogether.

*Caffeine and "Soft" Drinks.*—Recently the practice has sprung up of using caffeine as a constituent of certain drinks supplied at the soda-water fountains. Such drinks usually purport to be made from the kola nut, which contains caffeine, or to consist of extracts from the plants which yield cocoa and chocolate, when in reality they consist of artificial mixtures to which caffeine has been added. Those using these beverages are stimulated as they would be by tea or coffee and soon acquire the habit which makes them regular customers. Chief harm comes to the children who frequent the soda fountains and to those who, on account of constitutional tendencies, should avoid caffeine in all of its forms. It is generally understood that the so-called "soft" drinks are harmless. If this reputation is to be maintained, those containing caffeine must be excluded.

*Danger from Certain Medicinal Agents.*—Among the most valuable drugs used by the physician in the treatment of disease are several, such as morphine, chloral, and cocaine, which possess the habit-forming characteristic. Sad indeed are the cases in which some pernicious drug habit has been formed through the reckless administration of such medicines. Even the taking of such a drug as quinine as a "tonic" tends to develop a dependence upon stimulation which is equivalent to a habit. In the same list come also the drugs that are taken to relieve a frequently recurring indisposition, such as headache. The so-called headache powders are most harmful in their effects upon the nervous system and should be carefully avoided.(139)

*Stimulants in Health Unnecessary.*—Stimulants have been aptly styled "the whips of the nervous system." The healthy nervous system, however, like the well-disposed and well-fed horse, needs no whip, but is irritated and harmed through its use. Even in periods of weakness and depression, stimulants are usually not called for, but a more perfect provision for hygienic needs. Rest, relaxation, sleep, proper food, and avoidance of irritation, not stimulants, are the great restorers of the nervous system. A surplus of nervous energy gained through natural means is more conducive to health and effective work than any result that can possibly be secured through drugs. Then withal comes the satisfaction of knowing that one has the expression of his real self in the way in which he feels and in what he accomplishes—not a "whipped-up" condition that must be paid for by weakness or suffering later on.

*Summary.*—To solve the problem of keeping well, one must live the life which is in closest harmony with the plan of the body. Such a life, because of differences in physical organization, as well as differences in environment and occupation, cannot be the same for all. All, however, may observe the conditions under which the body can be used without injuring it and the special hygienic laws relative to the care of different organs. Causes of disease, whether they be in one's environment, vocation, in his use of foods or drugs, or in his mode of recreation, must either be avoided or counteracted.

While the problem is beset with such difficulties as lack of sufficient knowledge, inherited weakness, and time and opportunity for doing what is known to be best for the body, yet study and work that have for their aim the preservation or improvement of the health are always worth while. Health is its own reward. The expression of the poet,

"Each morn to feel a fresh delight to wake to life, To rise with bounding pulse to meet whate'er of work, of care, of strife, day brings to me,"

suggests the joy of being well. But the ultimate realization of one's aims and ambitions in life and the actual prolongation of one's period of usefulness are higher and more enduring rewards.

*Exercises.*—1. Summarize the different laws of hygiene. Upon what one fundamental law are these based?

2. State the important differences between a condition of health and one of disease.

3. In what general ways may disease originate in the body?

4. Describe a model sanitary home. With what special hygienic problems has the housekeeper to deal?

5. Describe a method of collecting a wholesome supply of cistern water. State possible objections to well and spring water.

6. What means may be employed in preventing the spread of contagious diseases?

7. By what means are malaria, typhoid fever, diphtheria, and tuberculosis spread from one individual to another?

8. Why are extra precautions necessary in the recovery from certain diseases, as typhoid fever, diphtheria, and scarlet fever?

9. How may one's vocation become a cause of disease? What conditions in the life of a student may, if uncounteracted, lead to poor health?

10. Of what special value are the parks and pleasure grounds in a city to the health of its inhabitants?

11. Discuss the hygienic value of work.

12. What conditions lead to the continuance of habit-forming substances after their use has become general?

13. How is it possible for one not using alcohol to be injured by this substance?

14. Discuss the effect of alcoholic abuse upon social environment.

15. Summarize the rewards of hygienic living.



SUMMARY OF PART II

For the maintenance of life the needs of the cells must be supplied and the body as a whole must be brought into proper relations with its surroundings. The last-named condition requires that the body be moved from place to place; that its parts be controlled and cooerdinated; and that it be adjusted in its various activities to external physical conditions. To accomplish these results there are employed:

1. The skeleton, or bony framework, which preserves the form of the body and supplies a number of mechanical devices, or machines, for causing a variety of special movements.

2. The muscular system, which supplies the energy necessary for executing the movements of the body.

3. The nervous system, which (a) controls and cooerdinates the various activities and (b) provides for the intelligent adjustment of the body to its environment. (Review Summary of Part I, page 215, and consult Fig. 92, page 214.)



APPENDIX

*Equipment.*—Nearly all of the apparatus and materials called for in this book may be found in the physical, chemical, and biological laboratories of the average high school. There should be ready, however, for frequent and convenient use, the following: One or more compound microscopes with two-thirds and one-fifth inch objectives; a set of prepared and mounted slides of the various tissues of the body; a set of dissecting instruments, including bone forceps; a mounted human skeleton and a manikin or a set of physiological charts; a set of simple chemical apparatus including bottles, flasks, test tubes, and evaporating dishes; and a Bunsen burner or some other means of supplying heat.

The few chemicals required may be obtained from a drug store or from the chemical laboratory. Access to a work bench having a set of carpenter's tools will enable one to prepare many simple pieces of apparatus as they are needed.

*Physiological Charts* are easily prepared by teachers or pupils by carefully enlarging the more important illustrations found in text-books or by working out original sketches and diagrams. These, if drawn on heavy Manila paper, may be hung on the wall as needed and preserved indefinitely. By the use of colors, necessary contrasts are drawn and emphasis placed on parts as desired. The author has for a number of years used such home-made charts in his teaching and has found them quite satisfactory. His plan has been to draw on heavy Manila paper, cut in sizes of two by three feet, the general outline in pencil and then to mark over this with the desired colors. There is of course an opportunity for producing results that are artistic as well as practical, and if one has time and artistic skill, better results can be obtained. Many of the cuts in this book are excellently suited to enlargement and, if properly executed, will provide a good set for general class purposes.

*Models.*—The use of prepared models of the different bodily organs is strongly urged. These may be so used in elementary courses as to obviate much of the dissections upon lower animals. Although the actual tissues cannot be so well portrayed, the general form and construction of organs are much better shown. Models well adapted to class or laboratory work are easily obtained through supply houses. Illustrations of several of these are shown in connection with the "Practical Work."



INDEX

Abdomen; dissection of, 169.

Abdominal cavity, 7, 138, 152.

Absorption, 173-186. Defined, 18, 173.

Accommodation, 379. To illustrate, 391.

Acid reactions, 171.

Acquired reflexes, 314.

Adipose tissue, 5, 178.

Afferent neurons, 296.

Air, 76. Changes it undergoes in lungs, 101. Complemental, 89, 103. Reserve, 89, 103. Residual, 89, 103. Tidal, 88, 103.

Air passages, 80.

Albuminoids, 119. Purpose served by, 121.

Alcohol, A cause of crime, 333. Effects on circulation, 55, 56. Effects on digestion, 167. Effects on energy supply, 195. Effects on respiratory organs, 98. Effects on social environment, 413. Effect on temperature regulation, 271. Effects on waste elimination, 212. General considerations, 412-415.

Alimentary canal, coats of, 138.

Alimentary muscles, work of, 159.

Alkaline reactions, 171.

Alveoli, 82.

Amylopsin, 155, 156.

Anatomy, defined, 1.

Animal heat, 192.

Anopheles, 401.

Antiseptic ointment, 275.

Antitoxin, 405.

Appetite, natural, 163.

Aqueous humor, 377.

Arachnoid, 299.

Arteries, 47. Bronchial, 84. Functions of, 51. Pulmonary, 84. Renal, 202. To illustrate elasticity of, 62. Why elastic, 48.

Articulations, 230-232. Kinds of, 230.

Assimilation, 18, 182.

Astigmatism, 384.

Atlas, 223.

Atoms, defined, 105.

Attraction sphere, 15.

Auditory canal, 358.

Auricles, 42.

Axis, 223.

Axis cylinder, 284.

Axon, 283. Form and length of, 284. Function of, 306. Structure of, 284.



Bacteria, 394.

Ball-and-socket joint, 231.

Basement membrane, 197.

Basilar membrane, 363.

Bathing, 272, 274.

Biceps muscle, action of, 263.

Bicuspids, 143.

Bile, 154, 155.

Binocular vision, 381.

Blind spot, 377. To prove presence of, 390.

Blood, 24-39. Changes in, 34. Checking flow from wounds, 58. Coagulation of, 31. Experiments with, 37-39. Flow of, how regulated, 50. Functions of, 33. Hygiene of, 34-36. Physical properties of, 24. Quantity of, 33. Supply to lungs, 82. Velocity of, 54. Where found, 24.

Blood platelets, 25.

Blood pressure, 52, 70.

Blood pressure and velocity, 52.

Blood vessels, to strengthen, 57.

Body, organization of, 19.

Bone groups, 223-229.

Bones, 216-242. Adaptation of, 228. Composition, 217. Gross structure of, 218. Minute structure of, 219. Observation on gross structure, 241. Properties of, 217. Table of, 229. To show composition of, 241. To show minute structure of, 242.

Bowels, rules for care of, 166.

Brachial plexus, 302.

Brain, 280, 288-291. Disturbed circulation, 327. Protection of, 299.

Brain workers, 408.

Breathing, see Respiration. Causes of shallow, 92. Illustrated, 87. To prevent shallow, 92.

Breathing exercises, 93.

Bronchus, 80.

Bulb, 291.



Caecum, 151, 158.

Calcium carbonate, 122.

Calcium phosphate, 122.

Calorie, defined, 126.

Cane sugar, 120.

Canines, 143.

Capillaries, 50, 64, 249. Blood pressure at, 70. Functions of, 51. Work of, 174.

Carbohydrates, 119, 125. Purpose served by, 121. Storage of, 177. Tests for, 135.

Carbon, 134.

Carbon dioxide, Final disposition of, 111. Preparation, 115. Pressure, 110. Properties, 110, 115.

Cardiac cycle, 46.

Cardiac orifice, 147.

Carpals, 227.

Carpus, 228.

Cell body, 283. Functions of, 305.

Cell-division, 16.

Cell nucleus, 14.

Cell reproduction, 16.

Cell structure, 14.

Cell surroundings, 17.

Cell wall, 15.

Cells, 13-23. Bone, how nourished, 220. Ciliated epithelial, 81. Food supply to, 180. General work of, 17. Importance of, 15. Passage of materials to, 183. Relation to nutrient fluid, 20. Specialized, 197. Special work of, 18. Striated muscle, 244.

Cerebellum, 290. Functions of, 317.

Cerebral functions, localization of, 318.

Cerebral hemispheres, 289.

Cerebral peduncles, 290.

Cerebrum, 288. Functions of, 317.

Chlorine, 135.

Cholesterine, 155.

Chordae tendineae, 43.

Choroid coat, 375.

Chyme, 150.

Cigarettes, 333.

Cilia, 81. To observe, 101.

Ciliary muscle, 375.

Ciliary processes, 375.

Circulation of blood, 40-64. Causes of, 54. Discovery of, by Harvey, 40. Divisions of, 51, 52. Effects of exercise upon, 63. Effects of gravity upon, 64. In a frog's foot, 64. Organs of, 40-54. Routes to, 174.

Coagulation, Causes of, 31. Purpose of, 32. Time required for, 33.

Cochlea, 362.

Coffee, Effects on complexion, 274. Effects on digestion, 167. Effects on heart, 56.

Colds, 193. Serious nature of, 94. To cure, 94.

Colon, parts of, 158.

Complexion, care of, 273.

Compound, defined, 104.

Conduction pathways, 286.

Conductivity, 304.

Condyloid joint, 232.

Conjunctiva, 373.

Consumption, see Tuberculosis.

Control of arteries, 319.

Convolutions, 289.

Cooerdination, defined, 279.

Cornea, 375.

Corpora quadrigemina, 290.

Corpora striata, 289.

Corpus callosum, 289, 293.

Cortex, 288, 294.

Coughing, 81.

Cranial cavity, 7, 225.

Cranial nerves, 296.

Crura cerebri, 290.

Crystalline lens, 380.

Culex, 402.

Cytoplasm, 15.



Defects in focusing, 383.

Deformities of skeleton, 233-236. Correction of, 236. Prevention of, 235.

Deglutition, 145. Steps in, 146.

Dendrites, 283, 306.

Dentine, 143.

Dermis, 264.

Dextrose, 30, 120, 150.

Diaphragm, 88. To illustrate action of, 102.

Diastole, 46.

Diaxonic neuron, 283.

Diet, one-sided, 124.

Diffusion, 371.

Digestion, 130-172. Hygiene of, 160. Nature of, 130. Not a simple process, 131. Of fat, 156. Purpose of, 177. Stomach, 148.

Digestive fluids, 132.

Digestive organs, 160. Table of, 138.

Digestive processes, 130, 141. Illustrated, 137.

Diphtheria, 94, 405. Care after, 211.

Disaccharides, 120.

Disease, 392-412. Causes of, 393. Eruptive, 405. Precautions in recovery from, 407. Prevention of, 393.

Dislocations, 239.

Dorsal-root ganglia, 295.

Drill, "setting up," 237.

Drugs, effects of, 35, 55, 129, 332.

Duodenum, 151.

Dura, 299.



Ear, 358. Hygiene of, 365. To demonstrate, 369.

Ear drum, 359.

Efferent neurons, 296.

Element, defined, 104.

Elevators of the ribs, 87.

Emetics, 151.

Emotional states, effects of, 330.

End bulbs, 342.

Endocardium, 42.

Endolymph, 361.

End-plate, 244.

End-to-end connections, 286.

Energy, 107, 186-196. Bodily control of, 192. From sun to cells, 191. How plants store sun's, 189. Increasing one's bodily, 194. In food and oxygen, 190. Kinds of, 186. Methods of storing, 187, 188. Transformation of, in muscle, 248, 249.

Enzymes, 132, 155. Of the tissues, 184.

Epidermis, 264, 266.

Epiglottis, 80, 354.

Epithelium, 139.

Eruptive diseases, 405.

Esophagus, 146.

Eustachian tube, 359.

Excessive reading, 331.

Excitant impulse, 305.

Excretion, 197-213. Defined, 18. Necessity for, 201.

Exercise, 256, 257, 328, 409. General rules for, 259. Results of, 257.

Exhaustion, nervous, 211. Results of, 195.

External ear, 358.

External stimuli, action of, 307.

Eye, 370-391.

Eyeball, 373. Chambers of, 377. Focusing power of, 378. Movements of, 381.

Eyelids, 373.

Eyes, Care of, 386. Removal of foreign bodies from, 387, Strong chemicals in, 388.

Eye strain, 211. And disease, 385.



Fat, 30, 149, 162. Digestion of, 156. Emulsification of, 157. Purpose served by, 121. Route taken by, 175. Tests for, 137. Where stored, 178.

Fatty acid, 156.

Fenestra ovalis, 361.

Fenestra rotunda, 363.

Ferments, see Enzymes.

Fibrin, 31.

Fibrin ferment, 32.

Fibrinogen, 30, 31.

Fissures, 289.

Food, 117-137. Advantages of coarse, 167. Classes of, 118, 119. Composition of, 124. Dangers from impure, 165. Defined, 117. Elements supplied by, 134. Excess of proteid, 208. Frequency of taking, 165. Materials, table of, 126, 126. Nitrogenous, 119. Order of taking, 161. Preparation of, 164. Purity of, 128. Quantity of, 164. Simple, 118. Variety, 128. With reference to digestive changes, 132.

Foot lever, diagram of, 253.

Foot-pound, 196.

Foot-wear, hygienic, 238.

Fractures, treatment of, 239.

Fumigation, 400.

Furniture, school, 236.



Gall bladder, 154.

Ganglia, 281. Dorsal-root, 295. Sympathetic, 298.

Gastric glands, 147.

Gastric juice, to illustrate action of, 172.

Gelatine, 218.

Germ diseases, avoidance of, 394.

Germs, 29, 394, 395. How spread, 395.

Glands, 197-213. Digestive, 140. Ductless, 208. Excretory, work of, 201. Gastric, 147. Kinds of, 197, 198. Lymphatic, 68, 208. Perspiratory, 206. Salivary, 144. Structure of, 197. Thymus, 208. Thyroid, 208.

Gliding joint, 232.

Glottis, 355.

Glycogen, 120, 177.

Grape sugar, tests for, 120, 136.

Gross anatomy, defined, 1.

Gullet, 146.

Gustatory pore, 345.

Gustatory stimulus, 345.



Habits, 315, 334.

Hair, 267. Care of, 276.

Hair cells, 363.

Hair follicle, 267.

Haversian canals, 219.

Hearing, defective, 366.

Heart, 41. Care of, 55. Connection with arteries and veins, 45. Difference in parts of, 44. How it does its work, 45. Observations on, 60, 61, 62. Sounds of the, 47. Valves of, 43.

Heart muscle, structure of, 247.

Heat and cold, effects of, 330.

Hemoglobin, 26.

Hepatic artery, 154.

Hepatic veins, 154.

Hindbrain, 290.

Hinge joint, 231.

Histology, defined, 1.

Humerus, 227.

Hyaloid membrane, 378.

Hydrochloric acid, 149, 150.

Hydrogen, 134.

Hygiene, Defined, 2. General aim of, 2. General laws of, 2, 392. Of digestion, 160. Of skeleton, 238. Relation of physiology and anatomy to, 3.

Hygienic housekeeping, 399.

Hypoglossal nerves, 298.



Ileo-caecal valve, 151.

Ileum, 151.

Images, Diagram illustrating, 372. Formation of, 371.

Incisors, 143.

Incus, 359.

Infectious diseases, 394.

Infundibula, 80, 84.