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KILLER GERMSMICROBES AND DISEASES THAT THREATEN HUMANITY
By Barry E. Zimmerman David J. Zimmerman
McGraw-HillCopyright © 2003 Barry E. Zimmerman and David J. Zimmerman
All right reserved.
Chapter OneThe Origin of Disease
Disease generally begins that equality which death completes.
Disease dates back nearly as far as life itself. To understand its origin, we must first understand the origin of life. Our planet formed from a contracting cloud of dust and gases about four and a half billion years ago. It was a hostile world of poisonous gases, erupting volcanoes, lightning bolts, and searing radiation from a newly formed star ninety-three million miles (150 million kilometers) away. The rock that formed its crust was molten and bubbling. To quote Lynn Margulis and Dorion Sagan from Microcosmos:
During these first years ... there was no solid ground, no oceans or lakes.... The planet was a molten lava fireball, burning with heat from the decay of radioactive elements in its core. The water of the Earth, shooting in steam geysers from the planet's interior, was so hot that it never fell to the surface as rain but remained high in the atmosphere, an uncondensable vapor. The atmosphere was thick with poisonous cyanide and formaldehyde. There was no breathable oxygen, nor any organisms capable of breathing it.
During these first years there were no living things, period. Yet one billion years later Earth was teeming with a simple form of microbial life. Evidence of these organisms has been found in Australia and Africa in banded domes of sedimentary rock called stromatolites. These stromatolites are thought to be the fossilized remains of layered mats of bacteria that were among the earliest living things. Sediments in Greenland date back 3.85 billion years. How did bacteria form from a bubbling cauldron of lava that was the infant Earth?
There are two possibilities: (1) Life arose from nonliving matter on Earth after it cooled and became a more hospitable place (terrestrial origin), or (2) life predates Earth, and the planet was "seeded" with spores from some dark and distant corner of our galaxy (extraterrestrial origin).
The consensus among scientists distinctly favors a terrestrial origin. Most astronomers consider the conditions in deep space too hostile for life to survive—even the highly durable spore stages of certain microorganisms. In space there is no air or air pressure, and the temperature is near absolute zero (-460°F or -273°C). When approaching a habitable and seedable planet such as Earth, radiation becomes intense from the nearby sun that provides the planet with needed warmth. Without a protective atmosphere the radiation is quickly lethal to living things. In fact in 1966 the hardiest of bacteria were carried aboard the spacecraft Gemini IX into Earth's orbit. None survived even six hours of direct exposure to the searing ultraviolet radiation of interplanetary space.
Also, no space seeds have ever been detected in the nearly half a century we have been trekking through the cosmos. Nor have they been found as part of any meteorite or on the surface of the moon or Mars—two places where we've landed and performed tests for biological activity. If they were common enough to seed our planet within the first billion years of its creation, they should be common enough to be detected somewhere out there now. The fact that they haven't leads scientists to believe that life—and germs—originated on Earth.
Three hundred fifty years ago it would not have been considered wrong to believe that maggots—slithering, sluglike creatures—formed spontaneously from rotting meat; or that frogs and snakes arose spontaneously from mud at the bottom of a pond; or that dirty old rags transformed into mice and rats; or that sperm injected into cucumbers turned into people. As late as the mid-1800s people believed that microorganisms arose spontaneously from broth or gravy or other spoiling foods. The concept that life can arise from nonlife by some wondrous and inexplicable metamorphosis is known as spontaneous generation.
Spontaneous generation explains the origin of life on Earth easily enough. Or rather, it accounts for the origin of life. There is not much explanation to spontaneous generation. Nonetheless, if organisms arose spontaneously, so be it; leave the explanations to philosophers and lawyers.
Except that under controlled scientific conditions that theory did not hold up. In 1668, in a classic set of experiments, Italian physician Francesco Redi proved conclusively that maggots did not arise spontaneously from rotting meat but from the invisibly small eggs laid by meat flies on the meat. The maggots were an intermediate, caterpillarlike stage in the life cycle of the flies.
Two hundred years later the great French microbiologist Louis Pasteur would prove conclusively that microorganisms did not arise spontaneously from gravy or other spoiling foods. His experiments would sound the death knell of spontaneous generation for all time. Living things must come from other living things. Even the simplest single-celled organisms need parents—or at least a parent.
This, however, creates a catch-22. If all living things must come from living things, and there were not living things on Earth in the beginning, where did the first living things come from? Obviously, they could not have had parents.
Just as obviously, they must have come from nonliving stuff—but not in the sense implied by spontaneous generation. There is a vast difference in concept. Spontaneous generation has been likened to the assembly of a Boeing 707 by a hurricane in a junkyard. The creation of life was a gradual process, taking many millions of years, requiring a constant supply of high energy that is no longer available and an atmospheric composition that no longer exists. Though it probably was a global affair, occurring over different portions of the primordial Earth in shallow tidal pools, or moist sections of clay, or hot-water deep-sea vents, it was not something that happened easily. And in all likelihood it has not offered an encore performance within the last few billion years.
Evolution of Life
The tedious process of matter's increasing in complexity from inorganic to organic to living is called chemical or prebiotic evolution—evolution before life. It is not a terribly recent concept. In the 1920s A. I. Oparin in Russia and J. B. S. Haldane in England independently postulated the chemosynthesis hypothesis—that conditions on the primitive Earth favored chemical reactions that would lead to the formation of more complex molecules and ultimately to the creation of life. These conditions included a poisonous mix of gases that did not contain oxygen and abundant energy in the form of solar radiation—ultraviolet in particular—lightning discharges, and heat from Earth's gravitational contraction and the decay of radioactive elements. These high-energy conditions no longer exist and haven't for several billion years.
To test the chemosynthesis hypothesis, scientists performed experiments during the 1950s and '60s in which they re-created conditions that existed on the primitive Earth. They duplicated the primordial atmosphere and charged it with energy in the form of heat and electricity for weeks at a time. They got more than one hundred organic compounds, including amino acids and proteins, sugars, and small bits of genetic material called nucleic acids—the building blocks of life!
The success of these experiments lent strong support to the hypothesis of chemical evolution. It is likely that, in its early history, Earth's lakes and oceans became a rich organic soup. Water is an ideal medium for molecules to splash around in and react. At some point in the process certain molecules developed the ability to line up amino acids and build proteins to order, and to make copies of themselves, so that the protein-making ability could be passed on. At another point this congregation of supermolecules separated themselves into microdroplets, bound in some way by a membrane, with the internal machinery to take in and use energy and to reproduce. Life on Earth had begun.
And the living things were bacteria—the most primitive of all cells. For the next two billion years bacteria would be the sole inhabitants of Earth, a reign unparalleled by any other living thing. They have persisted twenty-five times longer than the dinosaurs and two thousand times longer than humans. There are more bacteria in a handful of soil or inside your mouth than the total number of people that have ever lived. A single sneeze can carry with it a million bacteria. They make up 90 percent of the weight of human feces. Your body contains more bacterial cells than human cells—one hundred times as many! And they are found everywhere on earth—in the deepest oceans, on the highest mountain tops, even wafting along on high-altitude clouds.
The earliest cells were not initially parasitic. They lived free, feasting on the wealth of food in the seas, compliments of chemosynthesis. But they mutated in insidious ways and soon learned to invade free-living cells and cause disease—and changed forever the way life went on. Those that did not become parasitic evolved, in time, into all other living things—even the viruses, which are much simpler than the simplest bacteria. (Bacteria are the simplest cells, but viruses are not cells; they are merely a collection of molecules.) According to Rita Coswell of the University of Maryland, there are between three hundred thousand and one million different species of bacteria. Most are not pathogenic. But the handful that are, along with the viruses and parasites that they spawned, have caused untold misery and have dictated the course of human events.
Chapter TwoGerms and Disease: A Brief History
There are some remedies worse than the disease.
Languor seizes the body from bad ventilation.
Witchcraft, Retribution, and the Humor of It All
In 1831 a mad wolf charged through a small village in eastern France, jaws snapping, fangs bared, a poisonous lather spilling from its jowls. The wolf had just attacked the village blacksmith, badly mangling him. The man would survive the wounds; they would heal. In several months, however, he would be dead of rabies.
A boy of nine went home that day and asked his father, "What makes a wolf or a dog mad? Why do people die when mad dogs bite them?" His father, a village tanner, replied, "Perhaps a devil got into the wolf. If God wills you are to die, you will die." The boy who asked the questions was Louis Pasteur, and over the next half century he would answer them and many others.
Ignorance of the cause of disease prevailed throughout most of human history. People became ill because evil spirits entered their bodies. Through incantation and ritual dances and the use of various potions and arcane procedures, medicine men and witch doctors sought to drive out these spirits. If a patient whose body had been smeared with animal feces recovered, the shaman was revered as a great healer. If the patient died, it was not the fault of the doctor; the patient was paying for the sins that he had committed. King Tutankhamen, who died prematurely of tuberculosis, his lungs eaten away by the disease, was presumably paying for the sins of his father. It was a primitive concept of disease as divine retribution. People lived, they suffered, and they died. Humanity was virtually helpless in the face of the great plagues that periodically swept the land, killing or disabling millions of people.
Despite all of this futility, human ingenuity was never at a loss for preventive and curative measures. In Russia, to ward off pestilence, the townsfolk would hitch four widows to a plowshare and cut a furrow around their village in the dead of night (three widows would never do). King Louis XIV of France endured more than two thousand enemas during his seventy-two-year reign, to combat disease and to promote good health. (Known as le Roi Soleil—the Sun King—he might well have been called the "Moon" King, or Public Enema Number One.) George Washington, suffering from a sore throat and respiratory infection, was the recipient of "state-of-the-art" medical treatment in 1799. He was given a poisonous compound of mercury, by both mouth and injection. He was forced to ingest a poisonous white salt that made him perspire and vomit. Caustic poultices were applied to his body that made his skin blister. He was forced to inhale vinegar vapors that burned his lungs and raised blisters in his throat, to counteract the blisters of infection. As a final affront, more than five pints (2.4 liters) of blood were drained from his body. (An average-size male has ten or eleven pints—the volume of oil in the crankcase of your car.) All to no avail. He died shortly afterward—perhaps as much from the cure as from the illness.
The practice of removing blood from the body to combat disease was particularly popular. It was called bloodletting and was performed well into the nineteenth century. The treatment was based on a theory dating back to the teachings of Hippocrates in the fifth century B.C. People believed that the human body contained four fluids, or humors: blood, phlegm, yellow bile, and black bile. Hippocrates considered disease to be the result of an imbalance among these fluids. Sometimes the body could successfully restore the balance by itself, as evidenced by natural recovery from disease. At other times, however, the body needed help from a physician. Drawing blood from a patient was a favored approach (which was usually accomplished by cutting into a vein or applying leeches). In replenishing the lost blood, the body would somehow be stimulated to restore the proper balance of body fluids.
Before Washington, King Louis XV of France was the unfortunate recipient of similar medical wisdom. On the morning of April 27, 1774, he awoke quite ill. His body ached, and he was dizzy and feverish. Within a week ugly, pus-filled sores erupted on his face and neck and soon spread to the rest of his body. They filled his mouth and throat and caused great pain. He was suffering from a disease called smallpox, the terror of Europe and the New World. The royal medical team gathered and decided there was only one thing to do: the French monarch must be bled. He was exsanguinated until he lost consciousness (which was standard operating procedure); four large basinfuls of blood were removed from his body. No one can say whether the action hastened or delayed his death, which occurred on May 10. Such was the state of affairs in the medical community little more than two hundred years ago.
There were exceptions to this school of ignorance, but the perceptions of those with more progressive beliefs did not lead quickly to change. The germ theory was not formed all at once, like Athena springing full-grown and in full armor from the head of Zeus. To quote René Dubos, the great microbiologist and discoverer of the first antibiotic to be produced commercially: "The belief that microbes can cause disease had emerged as an abstract concept—a hunch—long before it was possible to state the facts clearly or to test them by experiment. Over many years, the theory evolved progressively from a vague awareness to the level of precise understanding" (Pasteur and Modern Science).
The roots of this understanding date back thousands of years. Virgil and Varro, citizens of the Roman Empire, said that some diseases were caused by invisible seeds. These seeds flew about in the air and were breathed in through the nose and mouth, causing infection and death. Sixteen hundred years later an Italian physician, Girolamo Fracastoro, suggested that syphilis was transmitted sexually by a contagium vivum, or "living agent." He outlined the different modes through which these living agents, and those of other diseases as well, could be spread: direct contact with an infected person, handling of contaminated materials, and breathing in infected air. About two hundred years later, in the mid-1700s, the Austrian physician Marcus von Plenciz theorized that not only were diseases caused by invisible living organisms but that each disease had its own particular culprit.
What marvelous insight. In the face of superstition and ignorance, of evil spirits and bloodletting, these men stood out as solitary candles in the darkness. Their tragic failing was that they did not offer proof. They did not subject their hunches and theories to controlled scientific experimentation. They did not collect data to back their claims. But there were great scientists on the horizon who would, people who would establish, through rigorous analysis, the germ theory of disease and usher in the Golden Age of Bacteriology—a span of about fifty years from the mid-1800s to the turn of the century.
Excerpted from KILLER GERMS by Barry E. Zimmerman David J. Zimmerman Copyright © 2003 by Barry E. Zimmerman and David J. Zimmerman. Excerpted by permission of McGraw-Hill. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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