The yellow, pink or purple spots developed upon the moist and moldy bread are caused by bacteria and yeast. Bacteria are one-celled organisms now classed as plants; they are the smallest known living beings, and can only be seen through a high power microscope.
Bacteria grow almost everywhere—in the soil, on all foods and fruits, in the water of ponds, streams and wells, in the mouths and stomachs of human beings, and in fact in almost all possible places, and occur in the air. Most of them are harmless, some of them are useful, and some produce disease in both plants and animals, including man.
What bacteria do would require many large volumes to enumerate. Some of them develop colors or pigments; some produce gases, often ill-smelling; some are phosphorescent; some take nitrogen from the air and fix it in the soil; some produce putrefaction; and some produce disease. Nearly all of the "catching diseases" are produced by bacteria. Diphtheria, scarlet fever, typhoid fever, consumption, influenza, grippe, colds, cholera, lockjaw, leprosy, blood poisoning and many other diseases are the result of bacteria. On the other hand, many of the bacteria are beneficial to man. Some forms ripen the cream before churning, others give flavor to butter; while some are an absolute necessity in making cheese. The making of cider into vinegar is the work of bacteria; some clear the pollution from ponds and streams; some help to decompose the dead bodies of animals, so that they return to the dust whence they came.
We have in our blood little cells whose business it is to destroy the harmful bacteria which get into the blood. These little fighting cells move everywhere with our blood, and if we keep healthy and vigorous by right living, right food and exercise, these cells may prove strong enough to kill the disease germs before they harm us. Direct sunlight also kills some of the bacteria. Seven or eight minutes exposure to bright sunlight is said to kill the germs of tuberculosis. Exposure to the air is also a help in subduing disease germs. Bichloride of mercury, carbolic acid, formaldehyde and burning sulphur also kill germs, and may be applied to clothing or to rooms in which patients suffering from these germ diseases have been. We can do much to protect ourselves from harmful bacteria by being very clean in our persons and in our homes, by bathing frequently and washing our hands with soap often. We should eat only pure and freshly cooked food, we should get plenty of sleep and admit the sunlight to our homes; we should spend all the time possible in the open air and be careful to drink pure water. If we are not sure that the water is pure, it should be boiled for twenty minutes and then cooled for drinking.
In Experiment A the milk vials and the corks are all boiled, so that we may be sure that no other bacteria than the ones we chose are present, since boiling kills these germs. As soon as the milk becomes discolored we know that it is full of bacteria.
Experiment B shows that bacteria can be transplanted to gelatin, which is a material favorable for its growth. But the point of this experiment is to show the child that a soiled finger will have upon it germs which, by growing, cloud the gelatin. They should thus learn the value of washing their hands often or of keeping their fingers out of their mouths.
Experiment C shows the way the destructive bacteria attack the potato. The discolored spots show where the decay begins, and the odor is suggestive of decay. If a potato thus attacked is put in the bright sunlight the bacteria are destroyed, and this should enforce the moral of the value of sunshine.
References—The Story of the Bacteria; Dust and its Dangers, M. T. Prudden, Putnam's. Bacteria in Relation to Country Life, Lipman.
Leading thought—Bacteria are such small plants that we cannot see them without the aid of a microscope, but they can be planted and will grow. The object of this lesson is to enforce cleanliness.
Experiment A—The bread used for the mold experiment is likely to develop spots of yellow, red or purple upon it, and cultures from these spots may be used in this lesson as follows: Take some vials, boil them and their corks, and nearly fill them with milk that has been boiled. Take the head of a pin or hairpin, sterilize the point by holding in a flame, let it cool, touch one of the yellow spots on the bread with the point, being careful to touch nothing else, and thrust the point with the bacteria on it into the milk; then cork the vials.
Experiment B—Prepare gelatin as for the table but do not sweeten. Pour some of this gelatin on clean plates or saucers. After it has cooled let one of the children touch lightly the gelatin in one saucer for a few seconds with his soiled finger. Note the place. Ask him to wash his hands thoroughly with soap and then apply a finger to the surface of the gelatin in the other plate. Cover both plates to keep out the dust and leave them for two or three days in a dark place. The plates touched by the soiled finger will show a clouded growth in the gelatin; the other plate will show a few irregular, scattered growths or none.
Experiment C—Take a slice of boiled potato, place in a saucer, leave it uncovered for a time or blow dust upon it, label with date, then cover with a tumbler to keep from drying and place in a cool, somewhat dark place.
The pupils should examine all these cultures every day and make the following notes:
Experiment A—How soon did you observe a change in the color of the milk? How can you tell when the milk is full of the bacteria? How do you know that the bacteria in the milk was transplanted by the pin?
Experiment B—Can you see that the gelatin is becoming clouded where the soiled finger touched it? This is a growth of the bacteria which were on the soiled finger.
Experiment C—What change has taken place in the appearance of the slice of potato? Are there any spots growing upon it? What is the odor? What makes the spots? Describe the shape of the spots. The color. Are any of them pimple-shaped? Make a drawing of the slice of potato showing the bacteria spots. What are the bacteria doing to the potato? Take a part of the slice of potato with the bacteria spots upon it, and put it in the sunshine. What happens? Compare this with the part kept in the dark.
After this lesson the children should be asked the following questions.
1. Why should the hands always be washed before eating?
2. Why should the finger nails be kept clean?
3. Why should we never bite the finger nails nor put the fingers in the mouth?
4. Why should we never put coins in the mouth?
5. Why should wounds be carefully cleansed and dressed at once?
6. Why should clothing, furniture and the house be kept free from dust?
7. Why should sweeping be done as far as possible without raising dust?
8. Why are hardwood floors more healthful than carpets?
9. Why is a damp cloth better than a feather duster for removing dust?
10. Why should the prohibition against spitting in public places be strictly enforced?
11. Why should the dishes, clothes and other articles used by sick persons be kept distinctly separate from those used by well members of the family?
12. Why should food not be exposed for sale on the street?
13. Why, during an epidemic, should water be boiled before drinking?
"This habit of looking first at what we call the beauty of objects is closely associated with the old conceit that everything is made to please man: man is only demanding his own. It is true that everything is man's because he may use it or enjoy it, but not because it was designed and 'made' for 'him' in the beginning. This notion that all things were made for man's special pleasure is colossal self-assurance. It has none of the humility of the psalmist, who exclaimed, 'What is man, that thou art mindful of him?'
—"The Nature Study Idea," L. H. Bailey.