Epidemic! The Natural History of Disease.  At the San Diego Natural History Museum

Experiment: Soapy Solutions

For all student levels; time: 1-2 hours
(Students working on their own, might want to check out a "Just for Kids" version of Soapy Solutions, also on this website.

When was the last time you washed your hands? Did you use soap? What have you done since you washed? Have you eaten, put your fingers in your mouth, or touched someone else?

Observations in public restrooms have revealed that only about 68 percent of Americans wash up before leaving. Yet thorough hand washing is one of the best ways to prevent the spread of infections. There are millions of microbes on your hands. Most are naturally occurring and harmless, but some may be disease-causing germs. Hand washing with soap lifts off those microbes and rinses them away. Hand washing with plain soaps or detergents suspends microorganisms and allows them to be rinsed off. Anti-bacterial soaps may potentially kill off harmless bacteria and may ultimately lead to the development and proliferation of resistant microorganisms.

Have students conduct an experiment to discover what is the most effective way to remove bacteria from your hands.

What You'll Need

Cooking oil, cinnamon, access to sink to wash hands, and measuring spoons. Ask 3 students to volunteer for the experiment.

What To Do For the student volunteers
1. Rub 1 tablespoon of cooking oil all over your hands until completely coated. Sprinkle 1 teaspoon of cinnamon on hands and rub it around until it's evenly distributed. The cinnamon will be like bacteria. It's all over!
2. Wash hands as follows, rubbing them briskly for 20 seconds:
Student #1: wash hands with cold water and no soap.
Student #2: wash hands with warm water and no soap.
Student #3: wash hands with warm water and soap.
3. For added variety, compare above methods by varying the time for rubbing hands, i.e., 5 seconds, 10 seconds, and 20 seconds. For simplicity, you may want to try this with 3 students washing hands with warm water and soap, method #3.

  For the rest of the class
1. Develop a hypothesis.
2. Observe the 3 hand-washing methods.
3. Record the results, looking for the amount of cinnamon (bacteria) that remains after the various washing methods. The method of hand washing that removed the most "bacteria" was .... The method that removed the least "bacteria" was ....
4. Illustrate how the hands of students 1, 2, and 3 looked after washing.
5. Draw conclusions.
I can remove bacteria from my hand by ....
If I used only cold water and no soap to wash, this is what might happen ....
Why does the warm water help? Soap? Rubbing?
How long does it take to get the bacteria washed off?

Questions for Discussion

1. How might hand washing affect your family's health?
You can spread germs to anyone or anything in your home that you touch. You can also get germs from objects other people have touched. If members of your family make an effort to wash often at appropriate times, you can help reduce the chances of each other getting ill.

2. What difference does soap make?
As the experiment showed, washing with water alone doesn't do as good a job as washing with soap. In the same way the soap lifts off the cinnamon so it can be rinsed away, soap grabs microbes so they're flushed away by the water. You just can't see it happen as easily with invisible microbes as you can with cinnamon.

3. What difference does the water temperature make? Warm water facilitates the soaping action on the hands so that it can more easily lift off the cinnamon "bacteria." It does not kill the bacteria, but makes it easier for the germs to be washed away with the vigorous rubbing of hands and fingers.

4. What infectious diseases could be spread by failure of people to adequately wash their hands?
There are many germs that can be spread or picked up through inadequate hand washing. For example, cold viruses can be spread by touching people or objects. The flu virus is often spread by contact with infected people. Salmonella, a bacterium that causes severe upset stomach, can be picked up from surfaces where raw foods--particularly meats--have been sitting. That's why hand washing not only protects you from illness, but also helps protect all those people you come into contact with.

Source: The Partnership for Food Safety Education, a unique public-private coalition of industry, government, and consumer groups created to reduce the incidence of food-borne illness by educating Americans about safe food handling practices. See www.fightbac.org.

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Fun with Fomites

Banner microbe: Adenovirus (virus causing common cold)
from the American Museum of Natural History Epidemic! exhibition

Teacher's Guide | Epidemic! | Exhibits