Science has made incredible progress in the last few centuries. The accelerated pace of discovery is clearly visible by the difference in the relative numbers of scientific disciplines today compared to the number back three or four hundred years ago. Many scientific discoveries have paved the way for the either the blending of scientific fields or the specialization of a scientific field. Microbiology, or the study of microorganisms and their effects on living creatures, is of the latter type.

Closely related to pathophysiology and the origin of disease, microbiology is a relatively new science. The advances and discoveries made by early microbiologists were so revolutionary that they clearly changed the way physicians and pathologists viewed the disease process and the living world. The revolutionary aspect of these discoveries can be compared to Newton’s discoveries or Einstein’s theories of relativity. However, it was many years before the fundamentals of microbiology were accepted by a wide majority of scientists.

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By examining the history and advancements in the field of microbiology, we can identify the individuals whose work had the greatest impact on the public acceptance of microbiology and the disease process in Europe in the 18th and 19th centuries. Early Beliefs The scientific field of microbiology actually has two separate origins; research into the true causes of illness and the debate over spontaneous generation. The medical beliefs in the 17th century were heavily influenced by the works of Galen and Aristotle9. Ancient Greeks believed that diseases were caused by the will of the gods.

Greek beliefs changed over time, and as physicians such as Hippocrates became better known. Galen (130-200 AD) was court physician to the Roman emperor and an influential medical scholar. Although the majority of his works were destroyed in a fire, many survived, including On Medical Experience. He supported and advanced Hippocrates four humor theory. This theory states that the body contains amounts of four different compounds: phlegm, blood, yellow bile, and black bile. These four substances, or humors, determine the health of a person. If they are relatively balanced, then the person should be in good health.

If any of these humors were to get out of balance, then illness would occur10. These beliefs lead to the rising popularity of bloodletting as a cure for some illnesses. The ratios of the four humors were also suggestive of the mood of the person; a person who was constantly depressed was determined to have an excess of black bile. Likewise, a person who was likely to lose their temper easily was said to have an excess of yellow bile. It was these beliefs in the internal cause of disease that misled future scientists and physicians in their research.

Although the four humor theory sounds illogical, early society did show signs of understanding diseases could be spread. A good example is the treatment of lepers, who were almost universally shunned. Quarantine became more and more common with many diseases. The Romans knew the benefits of keeping a clean water supply, and built huge aqueducts to bring fresh water from beyond the city’s pollution. The Roman system also assigned the office of “Water Commissioner” to ensure the water supply was kept clean. Polluters would be punished by death.

There are also many records which would suggest a nascent idea of immunity; those who had survived an illness were expected to help nurse the ill back to health11. The Black Death In the 14th century, a single disease wiped out a third of Europe’s population. Bubonic plague, commonly known at that time as the Black Death, is caused by the microbe Yersinia pestis. The plague is thought to have originated from China, and brought to Europe by traders. Infected individuals would develop red spots on their skin which would eventually turn black.

The illness is characterized with a high fever and a swelling of the lymph nodes, and was very acute and terminal in the middle ages. The medieval peasants and nobles were helpless against this unseen enemy; with no knowledge of germ vectors, they never realized that plague infected rats carried the disease. Fleas would spread the disease from rats to humans, and humans would spread the disease to members of their family and community. The number of victims declined in the winter months, as most fleas lie dormant due to the temperature.

Although the Black Death ravaged Europe on and off for the two centuries, it took its greatest death toll in its first five years, with 25 million dead. The Black Death brought two changes related to society’s beliefs about the nature of disease. Belief in the humor nature of illness was still strong but many questioned why those who seemed to be in perfect “balance” succumbed to this sickness. The other change was the belief that the plague was the punishment of a vengeful God, but when even the most devout succumbed to the illness, Christians began to doubt this belief4.

Debate on Spontaneous Generation In the 17th century the popular philosophy on the origin of life was the spontaneous generation theory. This belief was thought to have spread from ancient Egypt, where the Nile would flood its banks regularly. All kinds of creatures would remain dormant in the mud until the flood, and then rise, making it seem like they had “spontaneously” generated. Aristotle held this view, which persisted until it was challenged in Renaissance Europe1.

The spontaneous generation theory was modified to exclude humans and higher mammals, but lower forms of creatures, such as snakes, frogs, insects, and rats were capable of generating without parents. Researchers such as Baptiste von Helmont even claimed to have developed recipes for generating organisms. Helmont’s recipe for mice said to add wheat, barley, a little well water, and old dirty shirt to a wooden barrel and let it sit in a dark place. The barrel was not airtight by any means, and one can easily surmise that the mice would just as normally sneak into the barrel as be generated9.

Francesco Redi performed a simple experiment in 1650 that provided the evidence to reject spontaneous generation. He was looking for a recipe for making worms (maggots) from snake meat that he boiled. Instead of leaving the jars open to air, he tied cheesecloth around the top of one jar, and left one open to the air. The one open to the air was free for flies to come in and lay their eggs on, while the cheesecloth prevented the flies’ access. He then concluded that flies must produce the maggots, since no matter how long he left the cheesecloth bound sample of meat, no maggots would develop11.

The spontaneous generation theory began to be seriously questioned in the 1600s, and had it not been for the development of microscopes and the discoveries made thereafter, it likely would have been replaced. Emergence of Microscopes Magnifying lenses had been around for quite some time now, but there is a limit to how powerful a lens can be without a large amount of aberration. The Dutch father son duo of Hans and Zacharias Janssen are credited with the discovery of the compound microscope in the 1590s, a magnification device that uses an arrangement of lenses to magnify objects more than single lenses could.

This early microscope could magnify things from three to nine times their original size1. Although this was not a great enough magnification to see most microbes, greater importance is given to the fact that the theory of how the compound microscope used more than one lens was established. These early microscopes were also very expensive. It was a similar compound microscope with which the English scientist and member of the Royal Society Robert Hooke first viewed a piece of cork in 1660. As secretary of the Royal Society, he had to introduce a topic to discuss for their meeting.

As he was searching for interesting things to examine with the microscope at the meeting, a cork from a wine bottle grasped his attention. The cork seemed to be made of rectangular spaces arranged in lines, the lines then being stacked upon one another. Hooke gave these structures the name cells, after the spaces in a monastery where monks would transcribe documents. Hooke’s discussion at the meeting sparked a good deal of interest, and he later published Micrographia (1665), a book with the descriptions of other objects viewed under his microscope7. Antony van Leeuwenhoek

The next leap forward in discovery was prompted by Antony van Leeuwenhoek (1632-1723). The Dutchman from Delft, Holland was not a trained scientist, and had no higher education. He did not know Latin, or the language of science, and would most likely have been excluded from most scientific circles under normal circumstances. By trade he was a draper, a cloth merchant in 1654. After noticing some illustrations of various cloths under a microscope, Leeuwenhoek became very interested in magnification. Some historians claim that a copy of Hooke’s Micrographia might also have developed his interest in microscope.

The result was that Leeuwenhoek taught himself how to grind lenses and make his own microscopes. Unlike his predecessors, Leeuwenhoek did not utilize the compound microscope design. Most of his microscopes were a couple of inches long with a single lens, and two screws to allow one to focus the object. Leeuwenhoek’s choice to use a single lens in his microscope could come from the simplicity and efficiency of such a microscope, or his inability to design an effective compound microscope. However, his simple microscopes were made with lenses of such high quality that they magnified objects with much better magnification and clarity.

The best microscopes at the time could magnify objects thirty times their natural size; Leeuwenhoek’s microscope magnified an object over two hundred times its size. He is said to have made over five hundred microscopes in his lifetime, some of which could magnify objects three hundred to five hundred times their original size. Since many of his microscopes were made from silver and sometimes gold, the great majority of them were sold by his estate after his death. Ten of them survive today3. Leeuwenhoek’s microscopes were very good, but his discoveries are what got him the title of the first microbiologists.

Being a curious man, Leeuwenhoek would examine almost everything under his microscope. In 1676 Leeuwenhoek wrote to the Royal Society in London about his discoveries in a drop of rainwater. Leeuwenhoek was the first to see the microscopic life forms, such as the algae and protests in lake water. Leeuwenhoek also noticed these “animalcules” or “beasties” moving around, and were living microscopic creatures2. Although one might have thought the Royal Society would reject such a preposterous claim, Leeuwenhoek had actually been corresponding with them on the description of other structures, such as bee stings.

A few Royal Society members and witnesses of Leeuwenhoek’s discovery vouched for his discovery, and the Royal Society confirmed the presence of these creatures in 16776. Leeuwenhoek went on to describe protists, algae, sperm cells, and many other microscopic life forms. He was also the first person to view bacteria under a microscope, when comparing the plaque from the teeth of his wife and daughter who cleaned regularly and from two old men who did not clean their teeth. He described the three basic shapes of bacteria: coccus, bacillus, and spirochete. He wrote to Hooke about this observation.

The number of animalcules is small amount of ordinary substances seemed so large Leeuwenhoek commented “that all the water… seemed to be alive. ” He received full membership into the Royal Society in 1680, although he never attended their meetings in England. He received many noted visitors, including Tsar Peter the Great in 1698. He showed the Tsar how circulation in the capillaries of an eel took place. Leeuwenhoek’s microscopes and discoveries opened up a whole new world for research. The importance of such a discovery can be compared to discovering life on another planet; an invisible world teeming with microbes of great variety3.

Return of Spontaneous Generation Debate No one could explain where these microbes came from, or how they appeared on virtually everything. This lead to a revival of the spontaneous generation theory, with the exception that microbes could spontaneously generate, but higher life forms could not spontaneously appear. This view persisted for about a century after the discovery of microbes. Many theologists supported the spontaneous generation theory because the believed that God was still creating microscopic forms of life.

Researchers began to perform tests to see if spontaneous generation with microbes was valid. In the 1760s Lazzaro Spallanzani, an Italian scientist took a small glass round bottom flask and placed heated meat broth in them, and melted the glass shut. No bacterial growth could be detected in these broths, leading one to believe that bacteria could not spontaneously generate. Supporters of the spontaneous generation theory claimed that Spallanzani had made the flasks air tight, and that air was necessary for all life.

With every experiment that contradicted spontaneous generation, the proponents of the theory changed it to fit the circumstances, which eventually lead to the vital force theory. The vital force theory claims that an unknown force causes microbes to generate, but this force was retarded by heat, could not pass through glass, and needed air to produce bacteria. The great French scientist did a similar experiment to Spallanzani in which gun cotton was used to block the opening of the air passage instead of melted glass. Gun cotton is a cellulose nitrate derived compound that allows air to pass through, but acts much like a filter.

When he published his results, the vital force theory was changed to state that the vital force was retarded by heat, glass, and gun cotton. This heated debate continued until a scientific showdown in Paris9. Spontaneous Generation’s Last Stand The Frenchman Felix Pouchet had questioned spontaneous generation by performing an experiment like Spallanzani’s, but he used a hay infusion rather then a meat broth. He found that bacteria grew even after he boiled the infusion and sealed the glass shut. He perceived this as proof spontaneous generation was correct. Opposing him was the great Louis Pasteur.

In 1861 they were to perform their various experiments watched by other researchers and officials in Paris, within a given time frame, and then make the case for their results. The spontaneous generation theory suffered a large hit that day as Pouchet did not show up. No reason was given for his absence, and it is thought that the pressure of the competition drove him to run away. Had Felix Pouchet performed his hay infusion experiment, he most likely would have won the challenge8. Hay infusion commonly contains microbes that can form spores, or structures that resist high temperatures.

Thankfully his absence gave Pasteur even more credibility in front of the commission, who were slightly biased in favor of spontaneous generation. Pasteur’s final experiment in the spontaneous generation debate was the coup de grace. He would place sterile culture in a flask, on which he would affix a swan neck glass opening. Pasteur assumed correctly that microbes in the air were dependent on wind for most motion, so they would be trapped in the curve of the S shaped glass opening. No bacteria grew in his broths, and there are even a set of cultures Pasteur made that have not developed any growth even today.

Another important point to make is if the culture was tipped into the swan neck opening, bacteria would always grow in the culture. This proved that bacteria did not spontaneously generate, but grew from other bacteria. This was the proof that the majority of researchers and the public accepted as the nail in the coffin for spontaneous generation9. Advances in the Origin of Disease The rejection of the spontaneous generation theory by the public took quite a while and substantial evidence, and the acceptance of microorganisms as the cause of disease occurred not long afterwards.

In fact, Pasteur and the German Robert Koch, who finalizes the germ theory of disease, were competitive and nationalistic rivals. The background on the search for what causes illness is both colorful and informative. The first instance of an external factor involved in disease occurred in the 1830s. Italy had a thriving silk business at the time, and was profiting greatly with the Western demand for silk. Silk moths were used to cultivate the silk, the fiber of which actually comes from the cocoon that silk worms spin around themselves during metamorphosis.

After a while the worms began to stop emerging from the cocoons and died, which would ruin the silk fibers that were cultivated. The silk growers saw their profits begin to disappear, and hired a noted scientist to figure out why the worms were dying. Agostino Bassi performed his investigation from 1835-1844. During his investigation, he found that unclean cages had a fungus growing. He tested to see if the fungus were the cause of death and found that it was. He told the silk growers that they should clean their cages in hot water frequently, a practice they had followed earlier but stopped.

Bassi was hailed as a hero of Italy for saving the silk industry9. Bassi’s discovery was widespread, and many researchers heard about it. Ignatz Semmelweiss was an Austrian physician, specializing in obstetrics in Vienna. In 1841 he was hired to run a maternity ward in a hospital. The ward was split into two main sections: a section where midwives delivered the babies, and a section where the doctors delivered the children. Semmelweiss noticed the infection rate for mothers was higher in the doctor’s ward then it was in the midwives ward.

This infection known as child bed fever, or puerperal sepsis, killed more women in the doctor’s ward than in the midwives’ ward2. He also noticed that the midwives would wash their hands and arms before delivering the child, while the doctors, not wanting to drop the baby, would often spit chewing tobacco juice on their hands to get a better grip. When he claimed that this practice might be the cause of greater infection, there was an uproar among the doctors, and he was fired9. Semmelweis later saw a friend die from puerperal sepsis after cutting himself during the autopsy of a patient.

He published an article on how an unseen agent caused puerperal sepsis and how it could be transferred from doctors in the autopsy room to mothers in the maternity ward. He also recommended hand washing as a procedure for to limit infection. His work was not well received and he had to move from Vienna. He established cleanliness rules in other hospitals which lead to a decrease in the number of infections, but sadly Semmelweiss ended up in an asylum where he died from an infection that resembled puerperal sepsis2.

John Snow, an English physician, was next to carry on Semmelweiss work. He had read Semmelweiss’s articles and followed his practices. In 1849 a cholera outbreak ravaged much of England. Cholera is a frightening disease with the speed at which it takes effect. It induces incredible vomiting and almost continuous diarrhea; the danger is not specifically from the endotoxin the microbe produces, but from the dehydration which occurs rapidly. Snow saw the effects of cholera on his patients, and when cholera broke out five years later, he thought he knew the cause.

He had long believed that sewage mixed with water spread cholera, but his associates did not believe him. The governor of the area asked for Snow’s help after 350 people died in the next fifteen days. He began looking for similarities between the victims of the cholera. He was able to find out that all the victims had drunk water from a pump on Broad Street, which was also the epicenter of the epidemic. He told the governor to shut down the pump, which he reluctantly agreed to do, and the epidemic disappeared very quickly5.

Although his calls for better sewage system and methods to prevent contamination took a long time to be accepted, he is also noted as the first epidemiologist. Robert Koch The German Robert Koch heard about Snow’s study and was very interested by it. He was looking for an explanation for the disease anthrax, which occurred in rural areas in the 1880s. Koch noticed that farmers and fieldworkers often contracted topical or respiratory anthrax, and he performed isolating experiments until he isolated Bacillus anthracis as the culprit.

His work was not accepted at first, and he developed four confirmations known today as Koch’s postulates8. For most bacterial diseases, the following four evidences must be found to confirm that it is the pathogen: the microorganism must always be present in sick individuals and absent from healthy individuals; the microbe must be able to be isolated in a pure culture; a healthy individual must be infected with the microbe and similar illness should occur; and the microbe should be able to be isolated again from the second individual and compared to the original culture.

The scientific community decided that anthrax was a special case of microbial infection, but did not make the connection with other diseases9. On August 20, 1892 cholera broke out in Hamburg, Germany. These were almost perfect experimental conditions as Hamburg had a disease free sister city, Altona. Both of the water supplies for the cities were from the Elba River. However, Altona had installed a water filtration system, and Koch realized that all the cases occurred from drinking from the Hamburg water supply. Koch carried out his four postulates and identified Vibrio cholerae as the cause of cholera5.

This was undeniable proof that microbes could cause diseases, and by 1900 the scientific community and the public began to understand what actually caused diseases. Koch and Pasteur both went on to do more research in the field of microbiology, notably Pasteur’s namesake process, pasteurization. Conclusion Disease causing microorganisms are called pathogens. A side effect of the public acceptance of the microbial origin of disease was a misconception that all microbes are harmful. In fact, out of the microbes we know today, only five percent have any pathogenic tendencies for humans, livestock, or crops.

Although germ theory and the complete parental theory of life were unpopular ideas at first, when results were shown to scientists and the public, they gradually accepted it. Germ theory was harder to accept, although the changes brought about by changes in medical and sterile procedures saved so many lives that it was almost improbable to keep refuting it. The individuals who furthered the cause of microbiology and science the most in the public eye had to be the great scientists Robert Koch and Louis Pasteur.

Louis Pasteur was already a well respected scientist who’s simple but logical experiments left little room for doubt. He was also a popular figure in Parisian/French society, which led more public figures to believe in his work. Robert Koch, although not quite as charismatic as Pasteur, developed a process so foolproof to prove that an illness was caused by a pathogen; his work could rarely be refuted. Identifying a pathogen, and then infecting a healthy individual to gauge the effects was a dangerous task.

There were no chimpanzees or other test animals for Koch to test on, so he often tested the cultures on himself and later his laboratory workers. Few could argue with such testimony. Although other researchers such as John Snow, Joseph Lister, and Charles Chameberlain provided the methods for Koch’s work, and Spallanzani provided the method for Pasteur’s experiments, it was both Robert Koch and Louis Pasteur that had the greatest impact on the public acceptance of microbiology and the disease process in 18th and 19th centuries.