Germ, from the Latin "To Sprout"

Germ theory formally developed in the 1800s but the seed was planted long before.

 

An "animalcular" theory, published in 1658, can be found in Athanasius Kircher’s Scrutinium Physico–Medicum Contagiosae Luis. In the 19th century, the animacular theory was associated with an outdated past. The idea of tiny, invisible animals flying through the air and spreading disease seemed fanciful.

 

In miasma theory, diseases were caused by the presence in the air of a miasma, a poisonous vapor in which were suspended particles of decaying matter that was characterized by its foul smell. The theory originated in the Middle Ages and endured for several centuries. That a killer disease like malaria is so named - from the Italian mala ‘bad’ and aria ‘air’ - is evidence of its suspected miasmic origins.

Moreover in 19th-century England the miasma theory made sense to the sanitary reformers and fit with the notion of spontaneous generation.

 

Spontaneous generation—the theory that living organisms could arise from nonliving matter—was an important element in the early development of the germ theory. It was the obverse of germ theory and proponents of spontaneous generation argued the impossibility of knowing whether microorganisms found in these materials were the cause or the product of decomposition. Later debates around the role of germs in disease would be similar; it would take years to prove that germs found in the bodies of sick people were the cause of their disease and not the result of it.

Germ theory states that many diseases are caused by the presence and actions of specific micro-organisms within the body. Awareness of the physical existence of germs preceded the theory by more than two centuries. Discoveries made by several individuals also pointed the way to germ theory.

 

On constructing his first simple microscope in 1677, Antoni van Leeuwenhoek was surprised to see tiny organisms - which he called ‘animalcules’ - in the droplets of water he was examining. He made no connection with disease, and although later scientists observed germs in the blood of people suffering from disease, they suggested that the germs were an effect of the disease, rather than the cause. This fitted with the then popular theory of spontaneous generation.

 

Louis Pasteur (1822-1895) found that liquids such as beer and milk went bad because of the rapid multiplication of very small organisms - germs - in those liquids. He investigated further and found that many of these micro-organisms could be killed by heating the liquid: a preservation method now called ‘pasteurization’. He showed experimentally that the decay of meat was caused by microbes. The chemist argued that this could explain disease as well as decay, claiming that disease was caused by the multiplication of germs in the body. He went on to develop a new form of vaccination - by chance he discovered that germs which had been weakened by long exposure to the air caused immunity to cholera in chickens.

 

Ignaz Semmelweiss (1818-1865) was a Hungarian physician whose studies showed that maternal fever--often fatal--after childbirth was the result of contamination spread by the dirty hands of physicians from patient to patient and, often, from autopsies done right before delivery. Hand washing had a dramatic impact on infective illness.

 

Joseph Lister was present for the first operation done under anesthesia in 1846. He read Pasteur's work on micro-organisms and decided to experiment with using one of Pasteur's proposed techniques, that of exposing the wound to chemicals. He chose dressings soaked with carbolic acid (phenol) to cover the wound and the rate of infection was vastly reduced. Lister then experimented with hand-washing, sterilizing instruments and spraying carbolic in the theatre while operating, in order to limit infection.

 

John Snow (1813-1848) was famous for delivering the last two of Queen Victoria's children using anesthesia. But he is best known for his epidemiological evaluation of cholera. By recording the location of deaths related to a cholera outbreak in London in 1854, Snow was able to show that the majority were clustered around one particular public water pump in Broad Street, Soho; another blow against miasma.

 

Robert Koch first became known for his superior laboratory techniques in the 1870s, and is credited with proving that specific germs caused anthrax, cholera, and tuberculosis.  Koch's Postulates, which prove both that specific germs cause specific diseases and that disease germs transmit disease from one body to another, are fundamental to the germ theory.