Germ theory states that most infectious diseases are caused by microorganisms within the body. While the importance of sanitation in preventing the spread of disease is considered basic common sense today, germ theory only established itself around the mid-19th century.
The ancient Greeks had recognized that disease could be spread from person to person, but they were unsure how. The prevailing theory was that disease was caused by miasma – in other words, diseased air. In 1546, an Italian, Girolamo Fracastoro, described a prototype germ theory, but few medical professionals gave it serious consideration and although microorganisms were seen under the microscope for the first time in the 17th century, no clear link was made between them and disease. Then, in the 1840s, a Hungarian physician called Ignaz Semmelweis began to investigate the high death rates from puerperal fever on the maternity wards of a clinic where he worked.
The originator of antisepsis
When one of his medical colleagues died after a cut on his finger became infected during the dissection of a cadaver, Semmelweis came to a shattering conclusion. A large number of his obstetric staff were in the habit of studying dead bodies before going on their maternity rounds. Unaware of the danger posed by germs, they did not bother to wash their hands in between. These medical staff were inadvertent angels of death for the young women preparing to give birth. Semmelweis instituted a regime of cleaning with a chloride of lime wash. Its effect was immediate, with the death rate falling from 11.4 per cent to 1.2 per cent in a year. Soon the hygiene regime was extended to all members of staff and to objects as well. Semmelweis is thus the originator of antisepsis – the prevention of infection by arresting the growth and spread of germs. Yet Semmelweis would receive little credit for his life-saving leap of the imagination before his death in 1865.
Another early proponent of germ theory was English physician John Snow, whose many achievements included identifying a public water pump as the source of an outbreak of cholera in London in 1854. Meanwhile, in 1864 Louis Pasteur (1822–95) introduced pasteurization to the world – a process that kills the germs which cause food and drink to go off by heating them. A couple of years later, surgeon Joseph Lister published a landmark paper in which he detailed how carbolic acid could be used to kill germs and prevent infection of wounds.
Then, in the 1880s, German physician and pioneering microbiologist Robert Koch developed his ‘four postulates’ for establishing the relationship between specific organisms and diseases. He identified the bacterial causes of cholera, septicaemia and tuberculosis. In the same period, French microbiologist Charles Chamberland proved the existence of viruses (as distinct from bacteria) and Scottish doctor Patrick Manson investigated the role of vectors (for instance, mosquitoes and tsetse flies) in the spread of certain diseases. Thus armed with germ theory we became empowered to fight (and prevent) diseases in new, efficient ways.