Prior to the 16th century, most people (including scientists) thought that disease was caused by one of a variety of things: Beginning with Thomas Moffet in 1589, the vectors of disease began to be identified, and a variety of infections were identified as being caused by fungal invasion.

This led to Jenner's work on smallpox in 1796, leading to vaccination, and to Joseph Henle's postulates on parasites. Following this, Pasteur's work on micro-organisms and pasteurisation in 1857, led to an overall improvement in both social and medical cleanliness, with work from such as Joseph Lister and the development and use of antiseptic substances such as carbolic acid.

It is Pasteur who is considered to be the father of germ theory, bringing the theory of disease away from superstition and folklore into a more scientific arena. Although many in the medical profession still scoffed, many doctors and scientists began to take notice, and a great deal of careful research was carried out from the 17th Century onward. Robert Koch's work with anthrax began to expand the theory, and he made a number of discoveries and laid down many postulates:

  • The parasite must be present in every case of the disease
  • The parasite must not be present in any other disease as an agent not responsible for disease
  • The parasite must be capable of being isolated
  • After growth in pure culture, the parasite must be able to produce the disease
Koch also developed techniques to grow bacteria for study, and further developed methods of controlling the spread of bacteria through sterilisation. The field of bacteriology was born.

Many, most notably Christian Gram who developed a staining technique for classifying bacteria in 1884, continued to work and develop both theory and practice to both identify and treat infectious disease.

Nowadays, there are few who do not subscribe to modern germ theory, although many crank cures continue to be offered to a gullible public by quacks and charlatans.

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