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Most Dangerous Woman in America, The

Classroom Activity


To test the efficacy of different types of hand hygiene.

Materials for teacher
  • 2 14.5 oz. cans of sliced beets (10-12 slices per can)
  • can opener
  • 1 pair new plastic gloves
  • plastic forceps or tongs
  • isopropyl alcohol (for disinfecting)
Materials for each team
  • copy of the "Which Wash Wins?" student handout (PDF or HTML)
  • copy of the "Hand-Washing Methods" student handout (PDF or HTML)
  • 3 100 mm x 15 mm sterile plastic Petri dishes
  • cotton swabs
  • tape
  • permanent marker
  • access to sink with water (Teams 1, 2, and 3 only)
  • regular soap (Team 2 only)
  • antibacterial soap (with antiseptic like triclosan) (Team 3 only)
  • hand sanitizer (with ethyl or isopropyl alcohol) (Team 4 only)
  • paper towels (Teams 1, 2, and 3 only)

  1. Mary Mallon was a healthy carrier of the typhoid bacteria. Because she was a cook and handled food, she transmitted the disease to some of the people she worked for. Hand washing is one way to help stem the transmission of disease. In this activity students will test the efficacy of different types of hand hygiene.

  2. Prior to the activity, thoroughly disinfect the tongs by spraying or soaking them in alcohol (you may want to wash the can opener and tongs in a dishwasher and store them in a plastic bag prior to disinfecting). (Note: To increase the sterility of the experiment, consider using sterile agar plates instead of the beets.)

  3. Ask students if they have ever seen a sign in a restaurant bathroom that read: "Employees must wash hands." Why do students think these signs are there?

  4. Ask students what they think would be the best way to keep hands clean. What kinds of products, if any, do they think would be best? What water temperature? What amount of time spent washing? Write students' answers on the board.

  5. Tell students that they are going to test four methods a fifth group will serve as the control of hand hygiene (you may want to adapt these methods to reflect students' suggestions): 1) water only, 2) regular soap, 3) antibacterial soap, and 4) hand sanitizer.

  6. Organize students into five teams of four students each and provide each team with a set of materials. Each team will be assigned one of the following variables:

    Control Team: no washing method
    Experimental Team 1: washing with water only
    Experimental Team 2: washing with regular soap and water
    Experimental Team 3: washing with antibacterial soap and water
    Experimental Team 4: washing with hand sanitizer only

  7. Have each team develop a hypothesis of which of the four methods it thinks will work best and why. Then have students conduct the experiment as outlined in their handouts. As students start their hand-washing techniques, put on the plastic gloves and open the two cans of beets. Have each team use the tongs to retrieve three beet slices, one for each of the team's three Petri dishes. You may want to disinfect the tongs with alcohol between team uses.

  8. Have students record the results in a journal each day, making sure to include diagrams. After four days, compare the growth on the beets from the different teams. As a class, answer the following questions:

    • How did each set of beets compare to the control team's beets?

    • Which experimental team's beets had the least bacteria?

    • What areas (palms, in between fingers, under nails) were washed the most thoroughly by each technique? What areas were washed the least thoroughly?

    • Was there any growth on the control beets?

  9. Discuss the results with students. What results were most surprising? It's likely that all the beets showed some microbial growth because the experiment was not completely sterile. Discuss with students where microorganisms might have come from (beet, plastic tongs, cotton swab, Petri dish, tap water, air). How could the experiment have been made more sterile?

  10. To conclude, discuss with students why and when it is appropriate to wash hands.

  11. As an extension, have students research the controversy about whether using antibacterial soaps encourages the growth of new bacteria that are resistant to these products.

Beet Disposal

The beets used in this experiment should just contain normal molds and bacteria. The beet slices can remain in their Petri dishes and be disposed of in the regular trash. Spray with a disinfectant, such as Clorox, prior to disposing. Make sure students do not touch the beets after sealing their Petri dishes.

Activity Answer

You may want to review the following terms with students:

bacteria: microscopic, single- celled organisms that can be helpful or harmful to the human body

contagious: able to be transmitted to others, through direct or indirect contact

epidemiology: branch of medicine that studies the causes, distribution, and control of diseases in populations

infectious: capable of causing an infection

quarantine: enforced isolation or restriction of a person or persons to slow or halt the spread of a contagious disease

An individual can have an infection yet not be contagious. For more information on contagious diseases, including incubation and contagious periods for specific diseases, see

Molds and some kinds of bacteria are most likely to grow on the beets. The molds will probably look fuzzy green or white while the bacteria may be one of several colors (such as pink, yellow, or brown) or colorless and look shiny or dull. The bacteria are likely to grow in lawns (individual colonies that merge together to form a mat of bacteria). The beet provides the nutrients and water the bacteria and molds need to grow.

The growth on the beets provides evidence that microorganisms can be transmitted by hands. One strength of that evidence is that all of the control beets likely showed growth while the beets for the teams that used antibacterial soap and hand sanitizer likely showed less growth. One weakness is that the experiment was not entirely sterile; bacteria and mold from several sources could have contaminated the beets.

According to the Centers for Disease Control (CDC), plain soap is good at reducing bacterial counts, antibacterial soap is better, and an alcohol-based handrub is the best. However, students' results may vary depending on how well they washed their hands with each type of cleaner. You may want to repeat the experiment with students and have them wash their hands for a full minute and compare results of both trials.

Remind students that while their hands contain many harmless bacteria, they can also transmit bacteria and viruses that can cause illness. According to the Centers for Disease Control, one of the most important steps individuals can take to keep from getting sick is to wash their hands.

Both alcohol-based sanitizers and antibacterial soaps can kill harmful bacteria, such as streptococcus, salmonella, and E. coli, but do not claim to kill viruses (although some viruses are susceptible to these cleansers). Sanitizers work by using alcohol to kill the bacteria (they usually contain 60% to 95% ethanol or isopropanol). Antibacterial soaps rely on an antiseptic agent, such as triclosan, to kill the bacteria. Regular soap, which can remove bacteria through the action of its bubbles, is not designed to kill bacteria or viruses.

Hands should be washed at the following times: before, during, and after preparing food; before eating; after using the bathroom; after exposure to animals or animal waste; after handling garbage; after coughing, sneezing, or blowing your nose; and if you are sick or have been around a sick person.

Because bacteria can be transmitted to food, it is especially important that people involved with food preparation (as Mary Mallon was) frequently and properly wash their hands so they do not spread disease by fecal-oral transmission. For a full list of when food employees are supposed to wash, see

Links and Books

Web Sites

NOVA Web Site—The Most Dangerous Woman in America
Find articles, interviews, interactive activities, and resources in this companion Web site to the program.

The Living City
Reviews in time line format the life, health, and urban transformation of New York City during the decades between the end of the Civil War and the end of World War I.

Stalking the Mysterious Microbe
Provides background information on microbes and experiments.

Typhoid Mary
Reviews the story of Mary Mallon and provides links to additional information about typhoid fever.

What Should Be Done About Mary Mallon
Includes discussion questions related to Mary Mallon's case and provides access to related primary source documents.


Baker, S. Josephine. Fighting for Life. New York, Arno Press,1974 [c1939 ].
Provides an autobiographical look at the life and work of S. Josephine Baker, one of the first public health officers who approached Mary Mallon.

Bourdain, Anthony. Typhoid Mary: An Urban Historical. New York: Bloomsbury Publishing,2003.
Reveals the context in which Mary Mallon lived and the obstacles she faced as an Irish woman immigrant.

Diner, Hasia R. Erin's Daughters in America: Irish Immigrant Women in the Nineteenth Century. Baltimore: Johns Hopkins University Press, 1983.
Portrays the story of a group of Irish immigrant women who overcome barriers of poverty, ignorance, and disease to succeed in America.

Hammonds, Evelynn Maxine. Childhood's Deadly Scourge: The Campaign to Control Diphtheria in New York City,1880-1930. Baltimore: Johns Hopkins University Press,1999.
Explains how New York City became the first U.S. city to apply laboratory-based advances in bacteriology and immunology to the treatment and prevention of diphtheria.

Kraut, Alan M. Silent Travelers: Germs, Genes, and the "Immigrant Menace." New York: Basic Books,1994.
Covers immigration and health from a historical perspective, and includes accounts of how immigration and public health policies have influenced each other in the American experience.

Walzer Leavitt, Judith. Typhoid Mary: Captive to the Public's Health. Boston: Beacon Press,1996.
Explains the science of germ theory and explores the conflicting perspectives of the players in Mary Mallon's story, including journalists, public health officials, the law, and Mary herself. NOVA's "The Most Dangerous Woman in America" was based on this book.


The "Which Wash Wins?" activity aligns with the following National Science Education Standards:

Grades 5-8

Science in Personal and Social Perspectives

Science Standard F:
Science in Personal and Social Perspectives

Risks and benefits:

  • Individuals can use a systematic approach to thinking critically about risks and benefits. Examples include applying probability estimates to risks and comparing them to estimated personal and social benefits.

  • Important personal and social decisions are made based on perceptions of benefits and risks.

Grades 9-12

Science in Personal and Social Perspectives

Science Standard F:
Science in Personal and Social Perspectives

Personal and community health:

  • The severity of disease symptoms is dependent on many factors, such as human resistance and the virulence of the disease-producing organism. Many diseases can be prevented, controlled, or cured. Some diseases, such as cancer, result from specific body dysfunctions and cannot be transmitted.

Classroom Activity Author

Developed by WGBH Educational Outreach staff.

Teacher's Guide
Most Dangerous Woman in America, The

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