MiddleSchoolPortal/Turning Points in Science: Germ Theory

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Turning Points in Science: Germ Theory - Introduction

This is the first publication in our series called Turning Points in Science, which highlights the history and nature of science. The second publication covers the topic of Copernican revolution and the third, atomic theory.

The most exciting phrase to hear in science, the one that heralds the most discoveries, is not "Eureka!" (I found it!) but "That's funny." — Isaac Asimov

In 1989 the American Association for the Advancement of Science (AAAS) published Science for All Americans, which states,

. . . science education — meaning education in science, mathematics, and technology — should help students to develop the understandings and habits of mind they need to become compassionate human beings able to think for themselves and to face life head on. It should equip them also to participate thoughtfully with fellow citizens in building and protecting a society that is open, decent, and vital.



In 1996 the National Science Education Standards (NSES) was published, heavily influenced by Science for All Americans. For example, Science for All Americans contains chapters titled The Nature of Science and Historical Perspectives. You may be aware that the content standards of NSES include a domain title History and Nature of Science.

This publication, Turning Points in Science: Germ Theory, is the first in a series focused on historic, pivotal scientific advances, such as the discovery of germs, the Copernican model of the universe, and the elucidation of atomic theory. To avoid the pitfall of isolating the history and nature of science from science content, this series will focus on a specific advance relevant to the NSES content standards in life, physical, and earth sciences by examining the context of the science as thoroughly as possible. In this way, the science becomes understandable as a human endeavor; thus its impact on society is easily conceived. A potentially useful tool will be James Burke's Knowledge Web, which provides the connections between historic figures in science that enabled the advancement of science. Although a video explaining the tool is in Beta version only at the time of this writing, users can view it and bookmark the site for future use.

This publication also aims to facilitate student mastery of the Science as Inquiry standards. As students become aware of the methods of science, some unique to the various science disciplines, they will notice the unity in the use of logical argumentation based on empirical evidence. Researchers' personal accounts of their discoveries often fail to tightly align with the misnomer "the scientific method," and yet their findings have endured. Thus, we examine the status of the scientific concepts of interest at the point in history when the researchers’ findings joined the discussion: Who had made what claims, how, and why? What were the strengths and weaknesses of these claims? What were the competing hypotheses?

Middle school students’ conceptual understanding often recapitulates the history of science; their initial conceptions of natural phenomena are naive conceptions — explanations conjured up to account for their own experience with nature. For example, students often claim that aluminum foil is a good insulator because they have seen it used to wrap cans of pop in an attempt to keep the cans cold. The history of humanity shows similar kinds of misconceptions. For instance, the sun went around the earth, obviously; it rose every morning in the east and set every evening in the west. As another example of historic misconceptions, people thought necrotic tissue caused sickness. It was not conceivable that a nonvisible organism caused the sickness that resulted in necrotic tissue. Teachers can use student naive conceptions as a starting point.

This publication focuses on the elucidation of the germ theory of disease. This theory represents the culmination of the work of several individuals across time. Resources provided here will facilitate understanding of the early scientific community's concept of disease; the thinking that led to hypotheses relating germs to disease; the various observations and experiments that yielded information allowing for theorizing; the scientific community's reaction to and acceptance of the early investigators' findings; and the impacts of the theory on humanity.

In the Background Information for Teachers, resources include research articles on student naive conceptions and how to conduct inquiry teaching, a video description of the nature of scientific theory, followed by some history-related resources about important contributors to the germ theory of disease and their experiments. The two sections with lessons and activities are meant to facilitate student understanding of the context, the emergence, and the impact of the germ theory of disease. All of the resources touch on the NSES standards for History and Nature of Science, Science in Personal and Social Perspectives, Life Science, and Science as Inquiry. A very old, but accurate dramatization, The Story of Louis Pasteur is worth viewing by teachers. After viewing it yourself, you may consider encouraging your students to view it as enrichment.

An additional resource you may find helpful to use with your students is a book published by National Geographic Children's Books, Killing Germs, Saving Lives: The Quest for the First Vaccines. This title was selected by the National Science Teachers Association as one of the 2007 Outstanding Science Trade Books for Students K–12. The book, illustrated with prints and photographs, is told from a historical perspective and presents the work of scientists and healthcare providers who have observed, experimented, and accidentally discovered vaccines. The book demonstrates people’s changing ideas about diseases and the time needed for new discoveries. It also mentions ongoing efforts to find new vaccines. Check your local or school library or order a copy at the National Geographic Online Store.

Background Information for Teachers

Resources in this section focus on theory and historical background, but also include one link to workshops for teachers in microbiology. Teachers often have little time to get acquainted with the context and background of much of the content they are required to teach. We hope these resources save you time while providing you with helpful information that fills this information gap.

For guidelines on how to sequence your instruction use the NSDL Strand Map Service. These maps illustrate connections between concepts and across grade levels. An image of the middle grades (6-8) only part of the Discovering Germs map appears below. This map is one of nine under the heading Historical Perspectives. Clicking on a concept within the maps will show NSDL resources relevant to the concept, as well as information about related AAAS Project 2061 Benchmarks and National Science Education Standards. Move the pink box in the lower right hand corner of the page to see the grades 6-8 learning goals.

Discovery, Chance, and the Scientific Method This article on the nature of science discusses several events in science history and asks how chance influenced each. The authors conclude that though many textbooks credit serendipity, the reality is the scientists involved were probably aware of work done before them on until-then unanswered questions. They used this previous work to inform their own work and thus were enabled to make scientific progress, not by chance but by clever application, creativity and synthesis. These conclusions are consistent with this current study of the germ theory of disease.

Know the Difference A short video clarifies the different meanings of theory and hypothesis in science.

Germ Theory of Disease This outline provides an overview of the history of the germ theory of disease. Many of the key scientists and their work are mentioned, reinforcing the idea of how science advances by building on the work of others until a consistent pattern, comprising a theory, can be articulated.

A History of Science Volume IV A History of Science Volume IV This comprehensive volume covers almost all of chemical and biological science history. Chapter VII, “Eighteenth-Century Medicine”, and Chapter VIII, “Nineteenth-Century Medicine,” encompass development of the germ theory of disease.

2000 and Beyond: Confronting the Microbe Menace 2000 and Beyond: Confronting the Microbe Menace This page links to four excellent lectures. Those most relevant, lectures two and three, connect to the idea of antibiotic resistance and new lines of germ-combat research. We suggest choosing the option that displays the lecture and a synchronized slide show. Also, from the Animation button on the menu across the top of the page, we recommend the first three links under Infectious Disease: Bacterial Conjugation, E. coli Infection Strategy, and Intracellular Infection by Salmonella. These animations could be appropriate to show middle school students, but the written explanations will require modification in order to avoid inundating students with unfamiliar vocabulary.

Science Sampler: Correcting Student Misconceptions Before learning any formal science, children try to make sense of natural phenomena on their own. However, several studies have shown that it can be difficult to convince a student to give up a long-held misconception in favor of an accurate scientific explanation. Misconceptions can be confronted through hands-on and minds-on activities. The strategies outlined in this article will foster a climate of inquiry within the classroom. (Author’s Note: This article and the next three are from Science Scope, NSTA's middle school journal. Members access them for free, others can purchase them for $4.99 each. Teachers may also be able to find these articles for free through an online periodical service accessed through a school or local public library.)

The Scientific Method -- Is It Still Useful? Many scientists and science educators contend that a structured scientific method does not exist, while others might argue that the scientific method is too simplistic in its approach to scientific inquiry. This article addresses the dilemmas surrounding the scientific method, and provides suggestions that will enable you to meld the method with process skills.

Questioning Cycle: Making Students' Thinking Explicit During Scientific Inquiry Are you thinking about ways to get your students to think about science? Inquiry learning is an excellent way for students to get actively involved in science. Use the informative questioning cycle described in this article to ensure that students are making progress toward learning goals.

Science Sampler: Hypothesis-based Learning Are visions of students hypothesizing, designing experiments to test their explanations, analyzing data, writing formal publications of results, and debating over scientific procedures in an attempt to justify their control of variables dancing in your head? This dream can become a reality when you implement hypothesis-based learning. Follow the suggestions found in this article to put your dream in motion.

Lessons on the Historical Context

These lessons and activities will familiarize students with the life, times, and cultural contexts of the 19th and 20th centuries out of which emerged the germ theory of disease. By participating in some or all of these, students will obtain and likely retain conceptual understanding of not only the germ theory of disease but also the nature of science.

Teacher's Toolkit: Reforming Cookbook Labs This article presents 11 different ways of altering cookbook labs so that students understand the intention of the procedure, a step toward allowing more open-ended discovery. For example, given the procedure, students design a data table. Or, the steps in the procedure are mixed up and students have to put them in correct order. The suggested strategies can be applied to historic experiments, such as Redi's experiment to disprove spontaneous generation or Pasteur's swan-necked flask experiments. This approach contrasts with the normal presentation of these famous experiments where students are told what was done, how, why, and the results. Very often students do not understand why the methods were chosen or how the results are logical outcomes. Moreover, students rarely retain any significant conceptual understanding even though they were told the important points. (This online article is free to NSTA members; nonmembers must pay $4.99.)

Spontaneous Generation This lesson demonstrates that scientific knowledge is stable but also prone to change. Students will understand how those changes can happen in the context of the history of spontaneous generation. This lesson from the American Association for the Advancement of Science aligns with Benchmarks 1 and 10, Nature of Science and History of Science. It can be carried out as a class lesson or as an independent study. Part of the lesson involves students accessing related information on the Internet. Thorough teacher background information and pedagogically sound, structured discussion questions are provided.

No. 622: Ignaz Philipp Semmelweis The University of Houston's College of Engineering presents this series, called Engines of Ingenuity, about creative people and the machines "that make our civilization run." This episode is available in audio format. It recounts the story of Semmelweis's observations regarding contagious disease and the variables he believed could be controlled to prevent spreading of childbed fever.

No. 74: Germs Also from the series Engines of Ingenuity, this page recounts the contributions of various persons to the eventual development of the germ theory of disease.

Germy Surfaces In this Science Update from Science Netlinks, students will find out how long a germ can hang around and wait for its next victim.

Microbes 2: Louis Pasteur -- a Microbe Discoverer This site focuses on Pasteur and his discovery of microorganisms. Middle school students may not be able to imagine a world in which people did not know germs existed, because, in general, students have difficulty understanding that the beliefs, values, attitudes, and points of view of people in the past were different from those today.

Who Done It? Or What's That Brown Fuzzy Stuff on My Plum? Koch's Postulates for Proof of Pathogenicity A safe and simple exercise uses Koch's postulates to prove that an observed fungus is the cause of fruit disease. Since the fungus that causes brown rot of stone fruit (e.g., apricots, peaches, nectarines, plums, and cherries) is present naturally on the surface of these fruit, stone fruit purchased from the supermarket will usually develop the disease. The fungi responsible for brown rot are not human pathogens. This lab requires dissecting and compound microscopes. A simplified exercise, without cultures, to demonstrate the germ theory also is described.

Lessons on the Germ Theory in the 21st Century

Some say the germ theory of disease has been the most important medical breakthrough in history. It enabled the application of antibiotics in fighting disease. However, antibiotic resistance has emerged as a critical crisis. Does this render germ theory no longer useful? How does the germ theory of disease apply to modern disease control? This section focuses on future directions of managing germs and disease. Scientists are pursuing avenues with stronger emphasis on preventing disease rather than treating disease.

Science NetLinks: Science Update: Antibacterial Pollution Supermarket shelves groan under the weight of countless antibacterial products, but most of us have probably never stopped to consider what happens when these hand gels and dish soaps get washed down the drain. This resource gives an eye-opening look at the effect these products may have on fish and other wildlife. The site includes audio and a transcript of the Science Update radio spot, as well as a further explanation of the research behind the story and a set of discussion questions for use in the classroom. Links to related web resources are also provided.

Hero for Our Time This brief article highlights the context of Pasteur’s anthrax vaccine, its subsequent cascade effect in many fields of biology, and its relevance today. Links to additional resources are also available.

The Year 2000: Looking Back and Looking Forward This article gives a brief history of health care, including the elucidation of germ theory. In view of the explosion of technology and knowledge, the world should have become a very healthy and prosperous one. However, the existence of therapeutic options does not guarantee clinical impact. Patients must have access to these options and services.

Enough to Go Around: Edible Vaccines A great feature from the Why Files, this web site introduces the research of plant biologist Charles Arntzen of Arizona State University, a pioneer in the development of edible vaccines. Written in the Why Files’s entertaining and readable style, this easy-to-navigate web site explains how edible vaccines are made, how they work, and how they may significantly increase vaccination rates in developing countries. Relevant links to archived Why Files stories and other sources are provided.

Latest Science News from the New York Times

NYT > Bacteria

News about Bacteria, including commentary and archival articles published in The New York Times.

SMARTR: Virtual Learning Experiences for Students

Visit our student site SMARTR to find related science-focused virtual learning experiences for your students! The SMARTR learning experiences were designed both for and by middle school aged students. Students from around the country participated in every stage of SMARTR’s development and each of the learning experiences includes multimedia content including videos, simulations, games and virtual activities.


The FunWorks Visit the FunWorks STEM career website to learn more about a variety of science-related careers (click on the Science link at the bottom of the home page).

National Science Education Standards

Concepts of this publication align with the following National Science Education Standards.

History and Nature of Science: Content Standard G

Science as a Human Endeavor

  • Women and men of various social and ethnic backgrounds--and with diverse interests, talents, qualities, and motivations — engage in the activities of science, engineering, and related fields such as the health professions. Some scientists work in teams, and some work alone, but all communicate extensively with others.
  • Science requires different abilities, depending on such factors as the field of study and type of inquiry. Science is very much a human endeavor, and the work of science relies on basic human qualities, such as reasoning, insight, energy, skill, and creativity — as well as on scientific habits of mind, such as intellectual honesty, tolerance of ambiguity, skepticism, and openness to new ideas

Nature of Science

  • Scientists formulate and test their explanations of nature using observation, experiments, and theoretical and mathematical models. Although all scientific ideas are tentative and subject to change and improvement in principle, for most major ideas in science, there is much experimental and observational confirmation. Those ideas are not likely to change greatly in the future. Scientists do and have changed their ideas about nature when they encounter new experimental evidence that does not match their existing explanations.
  • In areas where active research is being pursued and in which there is not a great deal of experimental or observational evidence and understanding, it is normal for scientists to differ with one another about the interpretation of the evidence or theory being considered. Different scientists might publish conflicting experimental results or might draw different conclusions from the same data. Ideally, scientists acknowledge such conflict and work towards finding evidence that will resolve their disagreement.
  • It is part of scientific inquiry to evaluate the results of scientific investigations, experiments, observations, theoretical models, and the explanations proposed by other scientists. Evaluation includes reviewing the experimental procedures, examining the evidence, identifying faulty reasoning, pointing out statements that go beyond the evidence, and suggesting alternative explanations for the same observations. Although scientists may disagree about explanations of phenomena, about interpretations of data, or about the value of rival theories, they do agree that questioning, response to criticism, and open communication are integral to the process of science. As scientific knowledge evolves, major disagreements are eventually resolved through such interactions between scientists.

History of Science

  • Many individuals have contributed to the traditions of science. Studying some of these individuals provides further understanding of scientific inquiry, science as a human endeavor, the nature of science, and the relationships between science and society.
  • Tracing the history of science can show how difficult it was for scientific innovators to break through the accepted ideas of their time to reach the conclusions that we currently take for granted.

Science in Personal and Social Perspectives: Content Standard F

Personal Health

  • Sex drive is a natural human function that requires understanding. Sex is also a prominent means of transmitting diseases. The diseases can be prevented through a variety of precautions.
  • Natural environments may contain substances (for example, radon and lead) that are harmful to human beings. Maintaining environmental health involves establishing or monitoring quality standards related to use of soil, water, and air.

Risks and Benefits

  • Risk analysis considers the type of hazard and estimates the number of people that might be exposed and the number likely to suffer consequences. The results are used to determine the options for reducing or eliminating risks.
  • Students should understand the risks associated with natural hazards (fires, floods, tornadoes, hurricanes, earthquakes, and volcanic eruptions), with chemical hazards (pollutants in air, water, soil, and food), with biological hazards (pollen, viruses, bacterial, and parasites), social hazards (occupational safety and transportation), and with personal hazards (smoking, dieting, and drinking).
  • 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.

Science and Technology in Society

  • Science influences society through its knowledge and world view. Scientific knowledge and the procedures used by scientists influence the way many individuals in society think about themselves, others, and the environment. The effect of science on society is neither entirely beneficial nor entirely detrimental.
  • Societal challenges often inspire questions for scientific research, and social priorities often influence research priorities through the availability of funding for research.
  • Science cannot answer all questions and technology cannot solve all human problems or meet all human needs. Students should understand the difference between scientific and other questions. They should appreciate what science and technology can reasonably contribute to society and what they cannot do. For example, new technologies often will decrease some risks and increase others.

Life Science: Content Standard C

Structure and Function in Living Systems

  • All organisms are composed of cells--the fundamental unit of life. Most organisms are single cells; other organisms, including humans, are multicellular.
  • Cells carry on the many functions needed to sustain life. They grow and divide, thereby producing more cells. This requires that they take in nutrients, which they use to provide energy for the work that cells do and to make the materials that a cell or an organism needs.
  • Disease is a breakdown in structures or functions of an organism. Some diseases are the result of intrinsic failures of the system. Others are the result of damage by infection by other organisms.

Reproduction and Heredity

  • Reproduction is a characteristic of all living systems; because no individual organism lives forever, reproduction is essential to the continuation of every species. Some organisms reproduce asexually. Other organisms reproduce sexually.
  • Every organism requires a set of instructions for specifying its traits. Heredity is the passage of these instructions from one generation to another.
  • Hereditary information is contained in genes, located in the chromosomes of each cell. Each gene carries a single unit of information. An inherited trait of an individual can be determined by one or by many genes, and a single gene can influence more than one trait. A human cell contains many thousands of different genes.

Regulation and Behavior

  • An organism's behavior evolves through adaptation to its environment. How a species moves, obtains food, reproduces, and responds to danger are based in the species' evolutionary history.

Diversity and Adaptations of Organisms

  • Millions of species of animals, plants, and microorganisms are alive today. Although different species might look dissimilar, the unity among organisms becomes apparent from an analysis of internal structures, the similarity of their chemical processes, and the evidence of common ancestry.
  • Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.
  • Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; most of the species that have lived on the earth no longer exist.

Science as Inquiry: Content Standard A

Understandings about Scientific Inquiry

  • Different kinds of questions suggest different kinds of scientific investigations. Some investigations involve observing and describing objects, organisms, or events; some involve collecting specimens; some involve experiments; some involve seeking more information; some involve discovery of new objects and phenomena; and some involve making models.
  • Current scientific knowledge and understanding guide scientific investigations. Different scientific domains employ different methods, core theories, and standards to advance scientific knowledge and understanding.
  • Technology used to gather data enhances accuracy and allows scientists to analyze and quantify results of investigations.
  • Scientific explanations emphasize evidence, have logically consistent arguments, and use scientific principles, models, and theories. The scientific community accepts and uses such explanations until displaced by better scientific ones. When such displacement occurs, science advances.
  • Science advances through legitimate skepticism. Asking questions and querying other scientists' explanations is part of scientific inquiry. Scientists evaluate the explanations proposed by other scientists by examining evidence, comparing evidence, identifying faulty reasoning, pointing out statements that go beyond the evidence, and suggesting alternative explanations for the same observations.
  • Scientific investigations sometimes result in new ideas and phenomena for study, generate new methods or procedures for an investigation, or develop new technologies to improve the collection of data. All of these results can lead to new investigations.

Read the entire National Science Education Standards online for free or register to download the free PDF. The content standards are found in Chapter 6.

Author and Copyright

Mary LeFever is a resource specialist for the Middle School Portal 2: Math & Science Pathways project, a doctoral candidate in science education at Ohio State University, and presently teaches introductory biology at a Columbus, Ohio local high school. She has taught middle school and high school science and is an adjunct instructor of biology and natural sciences at Columbus State Community College.

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Copyright November 2007 - The Ohio State University. Last updated August 22, 2010. This material is based upon work supported by the National Science Foundation under Grant No. 0424671 and since September 1, 2009 Grant No. 0840824. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.