Germ theory of disease

From Wikipedia, the free encyclopedia

Scanning electron microscope image of Vibrio cholerae. This is the bacterium that causes cholera.

 

The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can lead to disease. These small organisms, too small to see without magnification, invade humans, other animals, and other living hosts. Their growth and reproduction within their hosts can cause disease. "Germ" may refer to not just a bacterium but to any type of microorganism or even non-living pathogen that can cause disease, such as protists, fungi, viruses, prions, or viroids. Diseases caused by pathogens are called infectious diseases. Even when a pathogen is the principal cause of a disease, environmental and hereditary factors often influence the severity of the disease, and whether a potential host individual becomes infected when exposed to the pathogen. 

The germ theory was proposed by Girolamo Fracastoro in 1546, and expanded upon by Marcus von Plenciz in 1762. Such views were held in disdain, however, and Galen's miasma theory remained dominant among scientists and doctors. The nature of this doctrine prevented them from understanding how diseases actually progressed, with predictable consequences. By the early nineteenth century, smallpox vaccination was commonplace in Europe, though doctors were unaware of how it worked or how to extend the principle to other diseases. Similar treatments had been prevalent in India from just before AD 1000. A transitional period began in the late 1850s with the work of Louis Pasteur. This work was later extended by Robert Koch in the 1880s. Viruses were discovered in the 1890s. By the end of the 1880s, the miasma theory was struggling to compete with the germ theory of disease. Eventually, a "golden era" of bacteriology ensued, during which the theory quickly led to the identification of the actual organisms that cause many diseases.

Miasma theory

A representation by Robert Seymour of the cholera epidemic depicts the spread of the disease in the form of poisonous air.

The miasma theory was the predominant theory of disease transmission before the germ theory took hold towards the end of the 19th century, and it is no longer accepted as a scientific theory of disease. It held that diseases such as cholera, chlamydia infection, or the Black Death were caused by a miasma (μίασμα, Ancient Greek: "pollution"), a noxious form of "bad air" emanating from rotting organic matter. Miasma was considered to be a poisonous vapor or mist filled with particles from decomposed matter (miasmata) that was identifiable by its foul smell. The theory posited that diseases were the product of environmental factors such as contaminated water, foul air, and poor hygienic conditions. Such infections, according to the theory, were not passed between individuals but would affect those within a locale that gave rise to such vapors.

Development

Pre-19th century

In Antiquity, the Greek historian Thucydides (c. 460 – c. 400 BC) was the first person to state, in his account of the plague of Athens, that diseases could spread from an infected person to others. One theory of the spread of contagious diseases that were not spread by direct contact was that they were spread by "seeds" (Latin: semina) that were present in the air. In his poem, De rerum natura (On the Nature of Things, c. 56 BC), the Roman poet Lucretius (c. 99 BC – c. 55 BC) stated that the world contained various "seeds", some of which could sicken a person if they were inhaled or if they contaminated his food. The Roman statesman Marcus Terentius Varro (116–27 BC) wrote, in his Rerum rusticarum libri III (Three Books on Agriculture, 36 BC): "Precautions must also be taken in the neighborhood of swamps […] because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases." The Greek physician Galen (AD 129 – c. 200/c. 216) speculated in his On Initial Causes (c. AD 175) that some patients might have "seeds of fever". In his On the Different Types of Fever (c. AD 175), Galen speculated that plagues were spread by "certain seeds of plague", which were present in the air. And in his Epidemics (c. AD 176–178), Galen explained that patients might relapse during recovery from a fever because some "seed of the disease" lurked in their bodies, which would cause a recurrence of the disease if the patients didn't follow a physician's therapeutic regimen.

During the Middle Ages, Isidore of Seville (c. 560–636) mentioned "plague-bearing seeds" (pestifera semina) in his On the Nature of Things (c. AD 613). Later in 1345, Tommaso del Garbo (c. 1305–1370) of Bologna, Italy mentioned Galen's "seeds of plague" in his work Commentaria non parum utilia in libros Galeni (Helpful commentaries on the books of Galen).

The Italian scholar and physician Girolamo Fracastoro proposed in 1546 in his book De Contagione et Contagiosis Morbis that epidemic diseases are caused by transferable seed-like entities (seminaria morbi) that transmit infection by direct or indirect contact, or even without contact over long distances. The diseases were categorised based on how they were transmitted, and how long they could lie dormant. 

Italian physician Francesco Redi provided early evidence against spontaneous generation. He devised an experiment in 1668 in which he used three jars. He placed a meatloaf and egg in each of the three jars. He had one of the jars open, another one tightly sealed, and the last one covered with gauze. After a few days, he observed that the meatloaf in the open jar was covered by maggots, and the jar covered with gauze had maggots on the surface of the gauze. However, the tightly sealed jar had no maggots inside or outside it. He also noticed that the maggots were found only on surfaces that were accessible by flies. From this he concluded that spontaneous generation is not a plausible theory.

Microorganisms are said to have been first directly observed in the 1670s by Anton van Leeuwenhoek, an early pioneer in microbiology. Yet Athanasius Kircher may have done so prior. When Rome was struck by the bubonic plague in 1656, Kircher spent days on end caring for the sick. Searching for a cure, Kircher observed microorganisms under the microscope and invented the germ theory of disease, which he outlined in his Scrutinium pestis physico-medicum (Rome 1658).^[16] Building on Leeuwenhoek's work, physician Nicolas Andry argued in 1700 that microorganisms he called "worms" were responsible for smallpox and other diseases.

In 1720, Richard Bradley theorised that the plague and 'all pestilential distempers' were caused by 'poisonous insects', living creatures viewable only with the help of microscopes.

In 1762, the Austrian physician Marcus Antonius von Plenciz (1705–1786) published a book titled Opera medico-physica. It outlined a theory of contagion stating that specific animalcules in the soil and the air were responsible for causing specific diseases. Von Plenciz noted the distinction between diseases which are both epidemic and contagious (like measles and dysentry), and diseases which are contagious but not epidemic (like rabies and leprosy). The book cites Anton van Leeuwenhoek to show how ubiquitous such animalcules are, and was unique for describing the presence of germs in ulcerating wounds. Ultimately, the theory espoused by von Plenciz was not accepted by the scientific community.

Agostino Bassi

The Italian Agostino Bassi was the first person to prove that a disease was caused by a microorganism when he conducted a series of experiments between 1808 and 1813, demonstrating that a "vegetable parasite" caused a disease in silkworms known as calcinaccio—this disease was devastating the French silk industry at the time. The "vegetable parasite" is now known to be a fungus pathogenic to insects called Beauveria bassiana (named after Bassi).

Ignaz Semmelweis

Ignaz Semmelweis, a Hungarian obstetrician working at the Vienna General Hospital (Allgemeines Krankenhaus) in 1847, noticed the dramatically high maternal mortality from puerperal fever following births assisted by doctors and medical students. However, those attended by midwives were relatively safe. Investigating further, Semmelweis made the connection between puerperal fever and examinations of delivering women by doctors, and further realized that these physicians had usually come directly from autopsies. Asserting that puerperal fever was a contagious disease and that matter from autopsies were implicated in its development, Semmelweis made doctors wash their hands with chlorinated lime water before examining pregnant women. He then documented a sudden reduction in the mortality rate from 18% to 2.2% over a period of a year. Despite this evidence, he and his theories were rejected by most of the contemporary medical establishment.

Gideon Mantell

Gideon Mantell, the Sussex doctor more famous for discovering dinosaur fossils, spent time with his microscope, and speculated in his Thoughts On Animalcules (1850) that perhaps "many of the most serious maladies which afflict humanity, are produced by peculiar states of invisible animalcular life".

John Snow

Original map by John Snow showing the clusters of cholera cases in the London epidemic of 1854

 

John Snow was a skeptic of the then-dominant miasma theory. Even though the germ theory of disease pioneered by Girolamo Fracastoro had not yet achieved full development or widespread currency, Snow demonstrated a clear understanding of germ theory in his writings. He first published his theory in an 1849 essay On the Mode of Communication of Cholera, in which he correctly suggested that the fecal-oral route was the mode of communication, and that the disease replicated itself in the lower intestines. He even proposed in his 1855 edition of the work, that the structure of cholera was that of a cell.

Having rejected effluvia and the poisoning of the blood in the first instance, and being led to the conclusion that the disease is something that acts directly on the alimentary canal, the excretions of the sick at once suggest themselves as containing some material which being accidentally swallowed might attach itself to the mucous membrane of the small intestines, and there multiply itself by appropriation of surrounding matter, in virtue of molecular changes going on within it, or capable of going on, as soon as it is placed in congenial circumstances.

— John Snow (1849)

For the morbid matter of cholera having the property of reproducing its own kind, must necessarily have some sort of structure, most likely that of a cell. It is no objection to this view that the structure of the cholera poison cannot be recognized by the microscope, for the matter of smallpox and of chancre can only be recognized by their effects, and not by their physical properties.

— John Snow (1855)

Snow's 1849 recommendation that water be "filtered and boiled before it is used" is one of the first practical applications of germ theory in the area of public health and is the antecedent to the modern boil-water advisory. 

In 1855 he published a second edition of his article, documenting his more elaborate investigation of the effect of the water supply in the Soho, London epidemic of 1854. 

By talking to local residents, he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow's chemical and microscope examination of a water sample from the Broad Street pump did not conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle. This action has been commonly credited as ending the outbreak, but Snow observed that the epidemic may have already been in rapid decline.

Snow later used a dot map to illustrate the cluster of cholera cases around the pump. He also used statistics to illustrate the connection between the quality of the water source and cholera cases. He showed that the Southwark and Vauxhall Waterworks Company was taking water from sewage-polluted sections of the Thames and delivering the water to homes, leading to an increased incidence of cholera. Snow's study was a major event in the history of public health and geography. It is regarded as one of the founding events of the science of epidemiology. 

Later, researchers discovered that this public well had been dug only three feet from an old cesspit, which had begun to leak fecal bacteria. The diapers of a baby, who had contracted cholera from another source, had been washed into this cesspit. Its opening was originally under a nearby house, which had been rebuilt farther away after a fire. The city had widened the street and the cesspit was lost. It was common at the time to have a cesspit under most homes. Most families tried to have their raw sewage collected and dumped in the Thames to prevent their cesspit from filling faster than the sewage could decompose into the soil.

After the cholera epidemic had subsided, government officials replaced the handle on the Broad Street pump. They had responded only to the urgent threat posed to the population, and afterward they rejected Snow's theory. To accept his proposal would have meant accepting the fecal-oral method transmission of disease, which they dismissed.

Louis Pasteur

Louis Pasteur’s pasteurization experiment illustrates the fact that the spoilage of liquid was caused by particles in the air rather than the air itself. These experiments were important pieces of evidence supporting the idea of germ theory of disease.

 

The more formal experiments on the relationship between germ and disease were conducted by Louis Pasteur between the year 1860 and 1864. He discovered the pathology of the puerperal fever and the pyogenic vibrio in the blood, and suggested using boric acid to kill these microorganisms before and after confinement.

Pasteur further demonstrated between 1860 and 1864 that fermentation and the growth of microorganisms in nutrient broths did not proceed by spontaneous generation. He exposed freshly boiled broth to air in vessels that contained a filter to stop all particles passing through to the growth medium, and even with no filter at all, with air being admitted via a long tortuous tube that would not pass dust particles. Nothing grew in the broths: therefore the living organisms that grew in such broths came from outside, as spores on dust, rather than being generated within the broth. 

Pasteur discovered that another serious disease of silkworms, pébrine, was caused by a small microscopic organism now known as Nosema bombycis (1870). Pasteur saved France's silk industry by developing a method to screen silkworms eggs for those that were not infected, a method that is still used today to control this and other silkworm diseases.

Robert Koch

Robert Koch is known for developing four basic criteria (known as Koch's postulates) for demonstrating, in a scientifically sound manner, that a disease is caused by a particular organism. These postulates grew out of his seminal work with anthrax using purified cultures of the pathogen that had been isolated from diseased animals.

Koch's postulates were developed in the 19th century as general guidelines to identify pathogens that could be isolated with the techniques of the day. Even in Koch's time, it was recognized that some infectious agents were clearly responsible for disease even though they did not fulfill all of the postulates. Attempts to rigidly apply Koch's postulates to the diagnosis of viral diseases in the late 19th century, at a time when viruses could not be seen or isolated in culture, may have impeded the early development of the field of virology. Currently, a number of infectious agents are accepted as the cause of disease despite their not fulfilling all of Koch's postulates. Therefore, while Koch's postulates retain historical importance and continue to inform the approach to microbiologic diagnosis, fulfillment of all four postulates is not required to demonstrate causality. 

Koch's postulates have also influenced scientists who examine microbial pathogenesis from a molecular point of view. In the 1980s, a molecular version of Koch's postulates was developed to guide the identification of microbial genes encoding virulence factors.

Koch's postulates:

1. The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
2. The microorganism must be isolated from a diseased organism and grown in pure culture.
3. The cultured microorganism should cause disease when introduced into a healthy organism.
4. The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

However, Koch abandoned the universalist requirement of the first postulate altogether when he discovered asymptomatic carriers of cholera and, later, of typhoid fever. Asymptomatic or subclinical infection carriers are now known to be a common feature of many infectious diseases, especially viruses such as polio, herpes simplex, HIV, and hepatitis C. As a specific example, all doctors and virologists agree that poliovirus causes paralysis in just a few infected subjects, and the success of the polio vaccine in preventing disease supports the conviction that the poliovirus is the causative agent.

The third postulate specifies "should", not "must", because as Koch himself proved in regard to both tuberculosis and cholera, not all organisms exposed to an infectious agent will acquire the infection. Noninfection may be due to such factors as general health and proper immune functioning; acquired immunity from previous exposure or vaccination; or genetic immunity, as with the resistance to malaria conferred by possessing at least one sickle cell allele.

The second postulate may also be suspended for certain microorganisms or entities that cannot (at the present time) be grown in pure culture, such as prions responsible for Creutzfeldt–Jakob disease. In summary, a body of evidence that satisfies Koch's postulates is sufficient but not necessary to establish causation.

Sanitation

In the 1870s, Joseph Lister was instrumental in developing practical applications of the germ theory of disease with respect to sanitation in medical settings and aseptic surgical techniques—partly through the use of carbolic acid (phenol) as an antiseptic.

Miasma theory (of disease)

From Wikipedia, the free encyclopedia

A representation by Robert Seymour of the cholera epidemic of the 19th century depicts the spread of the disease in the form of poisonous air.

 

The miasma theory (also called the miasmatic theory) is an obsolete medical theory that held diseases—such as cholera, chlamydia, or the Black Death—were caused by a miasma (μίασμα, ancient Greek: "pollution"), a noxious form of "bad air", also known as night air. The theory held that the origin of epidemics was due to a miasma, emanating from rotting organic matter. Though miasma theory is typically associated with the spread of disease, some academics in the early nineteenth century suggested that the theory extended to other conditions as well, e.g. one could become obese by inhaling the odor of food.

The miasma theory was accepted from ancient times in Europe and China. The theory was eventually given up by scientists and physicians after 1880, replaced by the germ theory of disease: specific germs, not miasma, caused specific diseases. However, cultural beliefs about getting rid of odor made the clean-up of waste a high priority for cities.

Etymology

The word miasma comes from ancient Greek and means "pollution". The idea also gave rise to the name malaria (literally "bad air") through medieval Italian.

Views worldwide

Book of Sebastian Petrycy published in Kraków in 1613 about prevention against "bad air".

Miasma was considered to be a poisonous vapor or mist filled with particles from decomposed matter (miasmata) that caused illnesses. The miasmatic position was that diseases were the product of environmental factors such as contaminated water, foul air, and poor hygienic conditions. Such infection was not passed between individuals but would affect individuals within the locale that gave rise to such vapors. It was identifiable by its foul smell. It was also initially believed that miasmas were propagated through worms from ulcers within those affected by a plague.

In India, there was also a miasma theory and the Indians take credit for being the first to put this miasma theory into clinical practice. The Indians invented paan, a gambir paste, that was believed to help prevent miasma; it was considered as the first antimiasmatic application. This gambir tree is found in Southern India and Sri Lanka.

In the 1st century BC, the Roman architectural writer Vitruvius described the potential effects of miasma (Latin nebula) from fetid swamplands when visiting a city:

For when the morning breezes blow toward the town at sunrise, if they bring with them mist from marshes and, mingled with the mist, the poisonous breath of creatures of the marshes to be wafted into the bodies of the inhabitants, they will make the site unhealthy.

The miasmatic theory of disease remained popular in the Middle Ages and a sense of effluvia contributed to Robert Boyle's Suspicions about the Hidden Realities of the Air.

In the 1850s, miasma was used to explain the spread of cholera in London and in Paris, partly justifying Haussmann's later renovation of the French capital. The disease was said to be preventable by cleansing and scouring of the body and items. Dr. William Farr, the assistant commissioner for the 1851 London census, was an important supporter of the miasma theory. He believed that cholera was transmitted by air, and that there was a deadly concentration of miasmata near the River Thames' banks. Such a belief was in part accepted because of the general lack of air quality in urbanized areas. The wide acceptance of miasma theory during the cholera outbreaks overshadowed the partially correct theory brought forth by John Snow that cholera was spread through water. This slowed the response to the major outbreaks in the Soho district of London and other areas. The Crimean War nurse Florence Nightingale (1820–1910) was a proponent of the theory and worked to make hospitals sanitary and fresh-smelling. It was stated in 'Notes on Nursing for the Labouring Classes' (1860) that Nightingale would "keep the air [the patient] breathes as pure as the external air.

Fear of miasma registered in many early nineteenth century warnings concerning what was termed “unhealthy fog”. The presence of fog strongly indicated the presence of miasma. The miasmas behaved like smoke or mist, blown with air currents, wafted by winds. It did not simply travel on air, it changed the air through which it propagated. The atmosphere was infected by miasma, as diseased people were. Many believed miasma was magical, and was able to change the properties of the air and atmosphere completely.

China

In China, miasma (Chinese: 瘴氣; pinyin: Zhàngqì; alternate names 瘴毒, 瘴癘) is an old concept of illness, used extensively by ancient Chinese local chronicles and works of literature. Miasma has different names in Chinese culture. Most of the explanations of miasma refer to it as a kind of sickness, or poison gas. 

The ancient Chinese thought that miasma was related to the environment of parts of Southern China. The miasma was thought to be caused by the heat, moisture and the dead air in the Southern Chinese mountains. They thought that insects’ waste polluted the air, the fog, and the water, and the virgin forest harbored a great environment for miasma to occur. 

In descriptions by ancient travelers, soldiers, or local officials (most of them are men of letters) of the phenomenon of miasma, fog, haze, dust, gas, or poison geological gassing were always mentioned. The miasma was thought to have caused a lot of diseases such as the cold, influenza, heat strokes, malaria, or dysentery. In the medical history of China, malaria had been referred to by different names in different dynasty periods. Poisoning and psittacosis were also called miasma in ancient China because they did not accurately understand the cause of disease. 

In the Sui dynasty, doctor Tsao Yuan-fung mentioned miasma in his book On Pathogen and Syndromes (諸病源候論). He thought that miasma in Southern China was similar to typhoid fever in Northern China. However, in his opinion, miasma was different from malaria and dysentery. In his book, he discussed dysentery in another chapter, and malaria in a single chapter. He also claimed that miasma caused various diseases, so he suggested that one should find apt and specific ways to resolve problems.

The concept of miasma developed in several stages. First, before the Western Jin Dynasty, the concept of miasma was gradually forming; at least, in the Eastern Han Dynasty, there was no description of miasma. During the Eastern Jin, large numbers of northern people moved south, and miasma was then recognized by men of letters and nobility. After the Sui and the Tang Dynasty, scholars-bureaucrats sent to be the local officials recorded and investigated miasma. As a result, the government became concerned about the severe cases and the causes of miasma by sending doctors to the areas of epidemic to research the disease and heal the patients. In the Ming Dynasty and Qing Dynasty, versions of local chronicles record different miasma in different places.

However, Southern China was highly developed in the Ming and Qing Dynasties. The environment changed rapidly, and after the 19th century, western science and medical knowledge were introduced into China, and people knew how to distinguish and deal with the disease. The concept of miasma therefore faded out due to the progress of medicine in China.

Influence in Southern China

The terrifying miasma diseases in the southern regions of China made it the primary location for relegating officials and sending criminals to exile since the Qin-Han Dynasty. Poet Han Yu (韓愈) of the Tang Dynasty, for example, wrote to his nephew who came to see him off after his banishment to the Chao Prefecture in his poem, En Route (左遷至藍關示姪孫湘):

At dawn I sent a single warning to the throne of the Nine Steps;
At evening I was banished to Chao Yang, eight thousand leagues.
Striving on behalf of a noble dynasty to expel an ignoble government,
How should I, withered and worn, deplore my future lot?
The clouds gather on Ch'in Mountains, I cannot see my home;
The snow bars the passes of Lan, my horse cannot go forward.
But I know that you will come from afar, to fulfil your set purpose,
And lovingly gather my bones, on the banks of that plague-stricken river.

The prevalent belief and predominant fear of the southern region with its "poisonous air and gases" is evident in historical documents. 

Similar topics and feelings toward the miasma-infected south are often reflected in early Chinese poetry and records. Most scholars of the time agreed that the geological environments in the south had a direct impact on the population composition and growth. Many historical records reflect that females were less prone to miasma infection, and mortality rates were much higher in the south, especially for the men. This directly influenced agriculture cultivation and the southern economy, as men were the engine of agriculture production. Zhou Qufei (周去非), a local magistrate from the Nan-Sung Dynasty described in his treatise, Representative Answers from the South: "... The men are short and tan, while the women were plump and seldom came down with illness," and exclaimed at the populous female population in the GuangXi region. 

This inherent environmental threat also prevented immigration from other regions. Hence, development in the damp and sultry south was much slower than in the north, where the dynasties' political power resided for much of early Chinese history.

Developments from 19th century onwards

Zymotic theory

Based on “zymotic” theory, people believed vapors called “miasmata” (singular: "miasma") rose from the soil and spread diseases. Miasmata were believed to come from rotting vegetation and foul water—especially in swamps and urban ghettos.

Many people, especially the weak or infirm, avoided breathing night air by going indoors and keeping windows and doors shut. In addition to ideas associated with zymotic theory, there was also a general fear that cold or cool air spread disease. The fear of night air gradually disappeared as understanding about disease increased as well as with improvements in home heating and ventilation. Particularly important was the understanding that the agent spreading malaria was the mosquitoes (active at night) rather than miasmata.

Contagionism versus miasmatism

Prior to the late 19th century, night air was considered dangerous in most Western cultures. Throughout the 19th century, the medical community was divided on the explanation for disease proliferation. On one side were the contagionists, believing disease was passed through physical contact, while others believed disease was present in the air in the form of miasma, and thus could proliferate without physical contact. Two members of the latter group were Dr. Thomas S. Smith and Florence Nightingale.

Thomas Southwood Smith spent many years comparing the miasmatic theory to contagionism.

To assume the method of propagation by touch, whether by the person or of infected articles, and to overlook that by the corruption of the air, is at once to increase the real danger, from exposure to noxious effluvia, and to divert attention from the true means of remedy and prevention.

Florence Nightingale:

The idea of "contagion", as explaining the spread of disease, appears to have been adopted at a time when, from the neglect of sanitary arrangements, epidemics attacked whole masses of people, and when men had ceased to consider that nature had any laws for her guidance. Beginning with the poets and historians, the word finally made its way into scientific nomenclature, where it has remained ever since [...] a satisfactory explanation for pestilence and an adequate excuse for non-exertion to prevent its recurrence.

The current germ theory accounts for disease proliferation by both direct and indirect physical contact.

Influence on sanitary engineering reforms

In the early nineteenth century, the living conditions of industrialized cities in Britain were increasingly unsanitary. Population was moving in much faster than the infrastructure could support. For example, the population of Manchester doubled within a single decade, leading to overcrowding and a great increase in waste accumulation.  The theory of miasma disease made sense to the sanitary reformers of the mid-19th century. Miasma explained why cholera and other diseases were epidemic in places where the water was undrained and very foul-smelling. As sanitary reform's engineering leader, London's Edwin Chadwick, asserted that "all smell is disease", and he proposed that a change in the fundamental structure of sanitation systems was in order to combat increasing urban mortality rates. Chadwick asserted that the problem of epidemics of cholera and typhoid was directly related to urbanization, and he proposed that new, independent sewer systems should be connected to homes. Chadwick supported his proposal with reports from the London Statistical Society which showed dramatic increases in both morbidity and mortality rates since the beginning of urbanization in the early nineteenth century. Though Chadwick proposed reform on the basis of miasma theory, his proposals still contributed to sanitation improvements, such as preventing the reflux of noxious air from sewers back into houses by separate drainage systems in the sanitation designs, which incidentally led to decreased episodes of cholera and thus helped to support the theory.

The miasma theory was consistent with the observations that disease was associated with poor sanitation (and hence foul odours) and that sanitary improvements reduced disease; it was not consistent with the observations of microbiology however which led to the later germ theory of disease. The introduction of medical bacteriology in the 1870s and 1880s provided a challenge to the miasma theory, though consensus was not reached immediately; concerns over sewer gas, which was a major component of the miasma theory developed by Galen and brought to prominence by the Great Stink, led to continuing proponents of the theory who observed that sewers enclosed the refuse of the human bowel, which medical science had discovered could teem with typhoid, cholera, and other microbes. 

The work of John Snow is notable for helping to make the connection between cholera and typhoid epidemics and contaminated water sources, which contributed to the eventual demise of miasma theory. During the cholera epidemic of 1854, Snow traced high mortality rates among the citizens of Soho to a water pump in Broad Street. Snow convinced the local government to remove the pump handle, which resulted in a marked decrease in cases of cholera in the area. In 1857, Snow submitted a paper to the British Medical Journal which attributed high numbers of cholera cases to water sources that were contaminated with human waste. Snow used statistical data to show that citizens who received their water from upstream sources were considerably less likely to develop cholera than those who received their water from downstream sources. Though his research supported his hypothesis that contaminated water, not foul air, was the source of cholera epidemics, a review committee concluded that Snow's findings were not significant enough to warrant change, and they were summarily dismissed. Additionally, other interests intervened in the process of reform. Many water companies and civic authorities pumped water directly from contaminated sources such as the Thames to public wells, and the idea of changing sources or implementing filtration techniques was an unattractive economic prospect. In the face of such economic interests, reform was slow to be adopted.

Even though later disproven by the influence of bacteria and the discovery of viruses, the miasma theory helped make the connection between poor sanitation and disease. This caused public health reforms and encouraged cleanliness, which in Britain led to the legislation of Parliament which approved the Public Health Acts of 1848 and 1858 and the Local Government Act of 1858. The latter of these confers the power of instating investigations into the health and sanitary regulations of any town or place, upon the petition of residents or death rates exceeding the norm. Early medical and sanitary engineering reformers included Henry Austin, Joseph Bazalgette, Edwin Chadwick, Frank Forster, Thomas Hawksley, William Haywood, Henry Letheby, Robert Rawlinson, Sir John Simon and Thomas Wicksteed. These and later British regulatory improvements were reported in the United States as early as 1865.

Particularly notable to nineteenth century sanitation reform is the work of Joseph Bazalgette, chief engineer to London's Metropolitan Board of Works. Encouraged by the Great Stink, Parliament sanctioned Bazalgette to design and construct a comprehensive system of sewers which intercepted London's sewage and diverted it away from its water supply. The system helped purify London's water supply and saved the city from epidemics. In 1866, the last of the three great British cholera epidemics took hold in a small area of Whitechapel. However, the area was not yet connected to Bazalgette's system, and the confined area of the epidemic in London acted as testament to the efficiency of the system's design.

Years later, the influence of these sanitary reforms on Britain was described by Sir Richard Rogers:

London was the first city to create a complex civic administration which could coordinate modern urban services, from public transport to housing, clean water to education. London's County Council was acknowledged as the most progressive metropolitan government in the world. Fifty years earlier, London had been the worst slum city of the industrialized world: over-crowded, congested, polluted and ridden with disease...

The miasma theory did contribute to containing disease in urban settlements, but did not allow for a suitable approach to safe excreta reuse in agriculture to be adopted. It was one of the causes for abandoning the prevailing practice of collecting human excreta from urban settlements and reusing them in the surrounding farmland (nowadays referred to as the ecosan approach of "closing the loop" when done in a safe manner). Such resource recovery schemes were common in many European cities until the 19th century before the arrival of sewer-based sanitation systems.

Throughout the nineteenth century public health, sanitation and the influence of miasma became the main reasons for the controversial practice of cremation. The miasma theory stated that infectious diseases were spread by noxious gases emitted from decaying organic matter, which included decaying corpses. This public health argument for cremation faded along with the miasma theory.

Replacement by germ theory

Although the connection between germ and disease was proposed quite early, it was not until the late-1800s that the germ theory was generally accepted. The miasmatic theory was challenged by John Snow, suggesting that there was some means by which the disease was spread via a poison or morbid material (orig: materies morbi) in the water. He suggested this before and in response to an epidemic on Broad Street in central London in 1854. Because of the miasmatic theory's predominance among Italian scientists, the discovery in the same year by Filippo Pacini of the bacillus that caused the disease was completely ignored. 

It was not until 1876 that Robert Koch proved that the bacterium Bacillus anthracis caused anthrax, which brought a definitive end to Miasma Theory.

In 1846, the Nuisances Removal and Diseases Prevention Act was passed to identify whether the transmission of Cholera is by air or by water. The bill was used to encourage the owner to clean their dwelling and connect them to sewers.

Some years later in 1855, John Snow made a testimony against the Amendment to this bill that regularized air pollution of some industries. He claimed that:

That is possible; but I believe that the poison of the cholera is either swallowed in water, or got directly from some other person in the family, or in the room; I believe it is quite an exception for it to be conveyed in the air; though if the matter gets dry it may be wafted a short distance.

At the same year, William Farr, who was then the major supporter of the Miasma Theory, issued a report to criticize the germ theory. Farr and the Committee wrote that:

After careful inquiry, we see no reason to adopt this belief. We do not feel it established that the water was contaminated in the manner alleged; nor is there before us any sufficient evidence to show whether inhabitants of that district, drinking from that well, suffered in proportion more than other inhabitants of the district who drank from other sources.

The more formal experiments on the relationship between germ and disease were conducted by Louis Pasteur between 1860 and 1864. He discovered the pathology of the puerperal fever and the pyogenic vibrio in the blood, and suggested using boric acid to kill these microorganisms before and after confinement. 

By 1866, eight years after the death of John Snow, William Farr publicly acknowledged that the miasma theory on the transmission of cholera was wrong, by his statistical justification on the death rate.

History of science in classical antiquity

From Wikipedia, the free encyclopedia

The Ptolemaic system of celestial motion, from Harmonia Macrocosmica, 1661.

 

The history of science in classical antiquity encompasses both those inquiries into the workings of the universe aimed at such practical goals as establishing a reliable calendar or determining how to cure a variety of illnesses and those abstract investigations known as natural philosophy. The ancient peoples who are considered the first scientists may have thought of themselves as natural philosophers, as practitioners of a skilled profession (for example, physicians), or as followers of a religious tradition (for example, temple healers). The encyclopedic works of Aristotle, Archimedes, Hippocrates, Galen, Ptolemy, Euclid, and others spread throughout the world. These works and the important commentaries on them were the wellspring of science.

Classical Greece

Practical knowledge

The practical concerns of the ancient Greeks to establish a calendar is first exemplified by the Works and Days of the Greek poet Hesiod, who lived around 700 BC. The Works and Days incorporated a calendar, in which the farmer was to regulate seasonal activities by the seasonal appearances and disappearances of the stars, as well as by the phases of the Moon which were held to be propitious or ominous. Around 450 BC we begin to see compilations of the seasonal appearances and disappearances of the stars in texts known as parapegmata, which were used to regulate the civil calendars of the Greek city-states on the basis of astronomical observations.

Medicine provides another example of practically oriented investigation of nature among the Ancient Greeks. It has been pointed out that Greek medicine was not the province of a single trained profession and there was no accepted method of qualification of licensing. Physicians in the Hippocratic tradition, temple healers associated with the cult of Asclepius, herb collectors, drug sellers, midwives, and gymnastic trainers all claimed to be qualified as healers in specific contexts and competed actively for patients. This rivalry among these competing traditions contributed to an active public debate about the causes and proper treatment of disease, and about the general methodological approaches of their rivals. In the Hippocratic text, On the Sacred Disease, which deals with the nature of epilepsy, the author attacks his rivals (temple healers) for their ignorance and for their love of gain. The author of this text seems modern and progressive when he insists that epilepsy has a natural cause, yet when he comes to explain what that cause is and what the proper treatment would be, his explanation is as short on specific evidence and his treatment as vague as that of his rivals.

There were several acute observers of natural phenomena, especially Aristotle and Theophrastus, who wrote extensively on animals and plants. Theophrastus also produced the first systematic attempt to classify minerals and rocks, summarised in the Naturalis Historia of Pliny the Elder in 77 AD. 

Ancient Greece was very advanced in Science & Technology. Thay produced theories about how the world works. There was a Hellenistic Age in Greek, in this Time the Greek culture spread throughout Persia, North Africa & Egypt.

Pre-Socratic philosophers

Materialist philosophers

The four classical elements (fire, air, water, earth) of Empedocles illustrated with a burning log. The log releases all four elements as it is destroyed.

 

The earliest Greek philosophers, known as the pre-Socratics, were materialists who provided alternative answers to the same question found in the myths of their neighbors: "How did the ordered cosmos in which we live come to be?" But although the question is much the same, their answers and their attitude towards the answers is markedly different. As reported by such later writers as Aristotle, their explanations tended to center on the material source of things.

Thales of Miletus (624–546 BC) considered that all things came to be from and find their sustenance in water. Anaximander (610–546 BC) then suggested that things could not come from a specific substance like water, but rather from something he called the "boundless." Exactly what he meant is uncertain but it has been suggested that it was boundless in its quantity, so that creation would not fail; in its qualities, so that it would not be overpowered by its contrary; in time, as it has no beginning or end; and in space, as it encompasses all things. Anaximenes (585–525 BC) returned to a concrete material substance, air, which could be altered by rarefaction and condensation. He adduced common observations (the wine stealer) to demonstrate that air was a substance and a simple experiment (breathing on one's hand) to show that it could be altered by rarefaction and condensation.

Heraclitus of Ephesus (about 535–475 BC), then maintained that change, rather than any substance was fundamental, although the element fire seemed to play a central role in this process. Finally, Empedocles of Acragas (490–430 BC), seems to have combined the views of his predecessors, asserting that there are four elements (Earth, Water, Air and Fire) which produce change by mixing and separating under the influence of two opposing "forces" that he called Love and Strife.

All these theories imply that matter is a continuous substance. Two Greek philosophers, Leucippus (first half of the 5th century BC) and Democritus of Abdera (lived about 410 BC) came up with the notion that there were two real entities: atoms, which were small indivisible particles of matter, and the void, which was the empty space in which matter was located. Although all the explanations from Thales to Democritus involve matter, what is more important is the fact that these rival explanations suggest an ongoing process of debate in which alternate theories were put forth and criticized. 

Xenophanes of Colophon prefigured paleontology and geology as he thought that periodically the earth and sea mix and turn all to mud, citing several fossils of sea creatures that he had seen.

Pythagoreans

The materialist explanations of the origins of the cosmos seems to miss an important point. It doesn't make much sense to think that an ordered universe comes out of a random collection of matter. How can a random assemblage of fire or water produce an ordered universe without the existence of some ordering principle? 

The first step in this emphasis upon a model was that of the followers of Pythagoras (approximately 582 – 507 BC), who saw number as the fundamental unchanging entity underlying all the structure of the universe. For Pythagoras and his followers matter was made up of ordered arrangements of point/atoms, arranged according to geometrical principles into triangles, squares, rectangles, and so on... Even on a larger scale, the parts of the universe were arranged on the principles of a musical scale and a number. For example, the Pythagoreans held that there were ten heavenly bodies because ten is a perfect number, the sum of 1 + 2 + 3 + 4. Thus with the Pythagoreans we find number emerging as the rational basis for an orderly universe — as the first proposal for a scientific ordering principle of the cosmos.

Plato and Aristotle

Plato (pointing up to heavenly things) and Aristotle (gesturing down to Earth). From Raphael, The School of Athens (1509)

 

Like the Pythagoreans, Plato (c. 427–c. 347 BC) found the ordering principle of the universe in mathematics, specifically in geometry. A later account has it that Plato had inscribed at the entrance to his school, the Academy, "Let no man ignorant of geometry enter." The story is a myth, but it has a grain of truth, for in his writings Plato repeatedly tells us of the importance of geometry. 

Plato is known more for his contributions to the philosophical basis of scientific method than to particular scientific concepts. He maintained that all things in the material world are imperfect reflections of eternal unchanging ideas, just as all mathematical diagrams are reflections of eternal unchanging mathematical truths. Since Plato believed that material things had an inferior kind of reality, he considered that we don't achieve demonstrative knowledge – that kind of knowledge we call science — by looking at the imperfect material world. Truth is to be found through rational demonstrations, analogous to the demonstrations of geometry. Applying this concept, Plato recommended that astronomy be studied in terms of geometrical models and proposed that the elements were particles constructed on a geometrical basis.

Aristotle (384–322 BC) disagreed with his teacher, Plato, in several important respects. While Aristotle agreed that truth must be eternal and unchanging, he maintained that we come to know the truth through the external world which we perceive with our senses. For Aristotle, directly observable things are real; ideas (or as he called them, forms) only exist as they express themselves in matter, such as in living things, or in the mind of an observer or artisan.

This theory of reality led to a radically different approach to science:

• First, Aristotle emphasized observation of the material entities which embody the forms.
• Second, he played down the importance of mathematics.
• Third, he emphasized the process of change where Plato had emphasized eternal unchanging ideas.
• Fourth, he reduced the importance of Plato's ideas to one of four causal factors.

As this last point suggests, Aristotle's concept of causes was less limited than ours. He distinguished four causes:

• The matter of which a thing was made (the material cause).
• The form into which it was made (the formal cause; something similar to Plato's ideas).
• The agent who made the thing (the moving or efficient cause).
• The purpose for which the thing was made (the final cause).

Aristotle's emphasis upon causes fundamentally shaped the later development of science by insisting that scientific knowledge, what the Greeks called episteme and the Romans scientia, is knowledge of necessary causes. He and his followers would not accept mere description or prediction as science. In view of this disagreement with Plato, Aristotle established his own school, the Lyceum, which further developed and transmitted his approach to the investigation of nature. 

Most characteristic of Aristotle's causes is his final cause, the purpose for which a thing is made. He came to this insight through his biological researches, in which he noted that the organs of animals serve a particular function.

The absence of chance and the serving of ends are found in the works of nature especially. And the end for the sake of which a thing has been constructed or has come to be belongs to what is beautiful.

Thus Aristotle was one of the most prolific natural philosophers of Antiquity. He made countless observations of the structure and habits of animals, especially those in the sea at Lesbos. He also made many observations about the large-scale workings of the universe, which led to his development of a comprehensive theory of physics. For example, he developed a version of the classical theory of the elements (earth, water, fire, air, and aether). In his theory, the light elements (fire and air) have a natural tendency to move away from the center of the universe while the heavy elements (earth and water) have a natural tendency to move toward the center of the universe, thereby forming a spherical earth. Since the celestial bodies – that is, the planets and stars – were seen to move in circles, he concluded that they must be made of a fifth element, which he called Aether.

Aristotle could point to the falling stone, rising flames, or pouring water to illustrate his theory. His laws of motion emphasized the common observation that friction was an omnipresent phenomenon – that any body in motion would, unless acted upon, come to rest. He also proposed that heavier objects fall faster, and that voids were impossible.

Theophrastus

Theophrastus noted that tourmaline attracts straws and bits of wood when heated.

 

Aristotle's successor at the Lyceum was Theophrastus, who wrote valuable books describing plant and animal life. His works are regarded as the first to put botany and zoology on a systematic footing. He also produced one of the very first works on mineralogy, with descriptions of ores and minerals known to the world at that time. He made some shrewd observations of their properties. For example, he made the first known reference to the phenomenon, now known to be caused by pyroelectricity, that the mineral tourmaline attracts straws and bits of wood when heated. Pliny the Elder makes clear references to his use of the work in his Natural History of 77 AD, while updating and making much new information available on minerals himself. From both these early texts was to emerge the science of mineralogy, and ultimately geology. Both authors describe the sources of the minerals they discuss in the various mines exploited in their time, so their works should be regarded not just as early scientific texts, but also important for the history of engineering and the history of technology. Pliny is especially significant because he provides full bibliographic details of the earlier authors and their works he uses and consults. Because his encyclopedia survived the Dark Ages, we know of these lost works, even if the texts themselves have disappeared. The book was one of the first to be printed in 1489, and became a standard reference work for Renaissance scholars, as well as an inspiration for the development of a scientific and rational approach to the world. 

The important legacy of this period of Greek science included substantial advances in factual knowledge, especially in anatomy, zoology, botany, mineralogy and astronomy; an awareness of the importance of certain scientific problems, especially those related to the problem of change and its causes; and a recognition of the methodological importance of applying mathematics to natural phenomena and of undertaking empirical research.

Hellenistic period

The military campaigns of Alexander the Great spread Greek thought to Egypt, Asia Minor, Persia, up to the Indus River. The resulting Hellenistic civilization produced seats of learning in Alexandria in Egypt and Antioch in Syria along with Greek speaking populations across several monarchies. Hellenistic science differed from Greek science in at least two ways: first, it benefited from the cross-fertilization of Greek ideas with those that had developed in the larger Hellenistic world; secondly, to some extent, it was supported by royal patrons in the kingdoms founded by Alexander's successors. Especially important to Hellenistic science was the city of Alexandria in Egypt, which became a major center of scientific research in the 3rd century BC. Two institutions established there during the reigns of Ptolemy I Soter (reigned 323–283 BC) and Ptolemy II Philadelphus (reigned 281–246 BC) were the Library and the Museum. Unlike Plato's Academy and Aristotle's Lyceum, these institutions were officially supported by the Ptolemies; although the extent of patronage could be precarious, depending on the policies of the current ruler.

Hellenistic scholars frequently employed the principles developed in earlier Greek thought: the application of mathematics and deliberate empirical research, in their scientific investigations.

The interpretation of Hellenistic science varies widely. At one extreme is the view of English classical scholar Cornford, who believed that "all the most important and original work was done in the three centuries from 600 to 300 BC". At the other end is the view of Italian physicist and mathematician Lucio Russo, who claims that the scientific method was actually born in the 3rd century BCE, only to be forgotten during the Roman period and not revived again until the Renaissance.

The Antikythera mechanism

The Antikythera mechanism.

 

The level of Hellenistic achievement in astronomy and engineering is impressively shown by the Antikythera mechanism (150–100 BCE). It is a 37-gear mechanical computer which computed the motions of the Sun and Moon, including lunar and solar eclipses predicted on the basis of astronomical periods believed to have been learned from the Babylonians. Devices of this sort are not known to have been engineered again until the 10th century, when a simpler eight-geared luni-solar calculator incorporated into an astrolabe was described by Persian scholar Al-Biruni. Similarly complex devices were also developed by other Muslim engineers and astronomers during the Middle Ages.

Herophilos

In medicine, Herophilos (335–280 BCE) was the first to base his conclusions on dissection of the human body and to describe the nervous system.

Archimedes, Apollonius, Euclid, Eratosthenes

Geometers such as Archimedes (c. 287 – 212 BCE), Apollonius of Perga (c. 262 – c. 190 BCE), and Euclid (c. 325 – 265 BCE), whose Elements became the most important textbook in mathematics until the 19th century, built upon the work of the Hellenic era Pythagoreans. Eratosthenes used his knowledge of geometry to measure the distance between the Sun and the Earth along with the size of the Earth.

Hipparchus

Astronomers like Hipparchus (c. 190 – c. 120 BCE) built upon the measurements of the Babylonian astronomers before him, to measure the precession of the Earth. Pliny reports that Hipparchus produced the first systematic star catalog after he observed a new star (it is uncertain whether this was a nova or a comet) and wished to preserve astronomical record of the stars, so that other new stars could be discovered. It has recently been claimed that a celestial globe based on Hipparchus's star catalog sits atop the broad shoulders of a large 2nd-century Roman statue known as the Farnese Atlas.

Roman Empire

Science in the Roman Empire period was concerned with systematizing knowledge gained in the preceding Hellenistic period and the knowledge from the vast areas the Romans had conquered. It was largely their work that would be passed on to later civilizations.

Even though science continued under the Roman Empire, Latin texts were mainly compilations drawing on earlier Greek work. Advanced scientific research and teaching continued to be carried on in Greek. Such Greek and Hellenistic works as survived were preserved and developed later in the Byzantine Empire and then in the Islamic world. Late Roman attempts to translate Greek writings into Latin had limited success, and direct knowledge of most ancient Greek texts only reached western Europe from the 12th century onwards.

Pliny

Pliny the Elder: an imaginative 19th-century portrait.

 

A mosquito and a fly in a Baltic amber necklace.

 

Of particular importance is the Naturalis Historia of Pliny the Elder published in 77 CE, one of the most extensive compilations of the natural world which survived the Dark Ages. Pliny does not simply list materials and objects but also seeks explanations of phenomena. Thus he is the first to correctly describe the origin of amber as being the fossilized resin of pine trees. He makes the inference from the observation of trapped insects within some amber samples. The Naturalis Historia divides neatly into the organic world of plants and animals, and the realm of inorganic matter, although there are frequent digressions in each section. He is especially interested in not just describing the occurrence of plants, animals and insects, but also their exploitation (or abuse) by man. The description of metals and minerals is particularly detailed, and valuable as being the most extensive compilation still available from the ancient world. Although much of the work was compiled by judicious use of written sources, Pliny gives an eye witness account of gold mining in Spain, where he was stationed as an officer.

Ptolemy

Ptolemy systematized the study of astronomy, drawing on the work of his predecessors to build astronomy upon a secure empirical basis and to demonstrate the relationship between astronomical observations and the resulting astronomical theory. His Almagest defined the method and subject matter of future astronomical research and the Ptolemaic system became the dominant model for the motions of the heavens.

Galen

In like manner, the Roman-era physician Galen codified and somewhat built upon Hellenistic knowledge of anatomy and physiology. His careful dissections and observations of dogs, pigs, and Barbary apes, his descriptions (based on these and the works of earlier authors) of such structures as the nervous system, heart, and kidneys, and his demonstrations that, for instance, arteries carry blood instead of air became a central part of medical knowledge for well over a thousand years.