Take the bottles out and allow them to cool. Remove the cotton from one of them for several minutes and then replace. Run a hat pin two or three times through the flame of a Bunsen burner to sterilize it and place it in the water of a vase which has had flowers in it for some time. Carefully pulling aside the edge of the absorbent-cotton stopper in the second bottle, insert the pin and place a drop of the vase water on the surface of the piece of potato. After having sterilized the pin again, rub it several times over the moistened palm of the hand and then, using the same precautions as before, scratch the potato in the third bottle. Keep the fourth bottle just as it was taken from the sterilizer, as an indicator, that is, to see whether the bottles were thoroughly sterilized. Put all of the bottles away in a warm place and observe them each day for several days. The spots appearing on the pieces of potato are bacteria colonies.
99.Bacteria. -The nitrogen-fixing bacteria were considered, to some extent, under soil, but, as these soil bacteria are but few in com- parison with the great number of species found existing almost ev- erywhere upon the earth"s surface, bacteria will be further considered here. In Experiment 113 we found that if substances are left exposed to the air they soon undergo certain changes, which they are free from when properly protected. These changes are due to bacteria.
The bacterium is a single-cell plant, probably the simplest of all plants; it can only be seen with a high-power microscope. Bacteria are rod shaped, thread-shaped, screw-shaped or have various other forms (Fig. 105). The protoplasm in the cell of bacteria has the power to assimilate food and build more protoplasm. When the cell has grown sufficiently, it divides into two cells.
A healthy bacterium grows fast enough to be ready to divide about once an hour. If it dividedonce an hour and each division continued toFig. 105.
divide once an hour, in the course of twenty-four hours there would be nearly seventeen million bacteria produced. If this were kept up for some weeks, the mass of bacteria would be as large as the earth. Of course, this would mean that each bacterium had plenty of room to live in and plenty of food to live on and nothing to injure it. These conditions are not found, and each bacterium has to struggle for existence just as every other plant does. As it is, however, bacteria are numberless.
Since bacteria and fungi cause the "spoiling" of food, it is necessary to find means of stopping their growth. It has been found that thoroughly smoking fish and meat preserves it; that salt acts as a preservative; that if fruit is heated to a boiling temperature and tightly sealed in cans it will keep, and that fruits do not spoil if placed in strong sugar sirups.
These and many other methods are used to keep bacteria away from food and to prepare the food in such a way that bacteria cannot live in it. It is found that bacteria do not thrive as well if placed where it is cold, so foods are kept in cold places. Many bacteria cannot stand thePREPARING SMOKED FISH AT GLOUCESTER.
sunlight; that is one of the reasons why it is so much more healthful to live in sunny rooms.
Steam is sufficient to kill bacteria as they usually exist. Under some conditions they can, however, withstand a greater temperature than that required to boil water. We found that they did not pass through absorbent cotton. It has been discovered that certain substances, like formaldehyde and hydrogen peroxide, prevent their growth. These substances are called disinfectants.
Certain bacteria thrive in the living flesh; it is therefore necessaryto disinfect cuts or else blood poisoning, which is a bacterial disease, may set in. Sometimes when a rusty nail is run into the hand or foot, if the wound is not properly disinfected and cared for, lockjaw, another bacterial disease, is developed. After a wound is disinfected, it is usually dressed with absorbent cotton in order to keep out the bacteria.
Bacteria are the cause of many diseases, such as pneumonia, tuberculosis, smallpox, typhoid fever and others. People having diseases of these kinds throw off great quantities of bacteria, usually called germs. If such germs are breathed into the lungs or swallowed into the stomach and intestines of other people, they give them these diseases. It is necessary, therefore, in diseases of this kind to take every precaution that the germs shall not be scattered abroad.
Tuberculous patients should be exceedingly careful to use individual dishes, to cover their mouths with cloths when sneezing or coughing, otherwise they will scatter vast numbers of disease germs and become a menace to society. Although thousands are afflicted each year with tuberculosis, largely through the carelessness of those having the disease, it is a readily preventable and curable disease. The vile and dangerous habit of spitting should be abolished everywhere and public drinking cups and towels should be abolished.
When diseases are very virulent, like smallpox or diphtheria, the patients are usually kept by themselves, quarantined, their rooms kept disinfected and every precaution taken that people who are susceptible to the disease shall not be exposed to the germs.
When disease bacteria get established in the system, they secrete a poison called toxin, which is absorbed by the blood and carried throughout the body, thus poisoning many other parts beside those immediately attacked by the bacteria. The cells of the body at once begin to secrete a substance to counteract this poison, an antitoxin. If the vitality of the patient is great enough, sufficient antitoxin will be secreted to neutralize the effect of the toxin and the disease will be overcome.
