VARIOLATION and VACCINATION: In the last half of the 17th Century the medical approach to controlling the devasting effects of smallpox was to treat healthy subjects with a mild strain of the disease . The smallpox sample consisting of the exudate of pustules from a patient suffering from smallpox, was applied through an incision in a recipient’s skin. This treatment was termed “variolation” (from variola; smallpox). Under the best conditions, variolated patients were maintained in isolated quarters until the infection passed. Most patients suffered a mild case of smallpox and were then immune to the disease. Unfortunately, the cost of variolation was high so that less well-off patients were not isolated. Rather,they were discharged and returned to their communities where they contributed to the spread of the disease. One of the great advantages of inoculation with cowpox virus was that immunity was induced without such patients introducing smallpox into the general population. The term “vaccination” (from vacca; cow) came into use in the smallpox literature In order to differentiate treatment with cowpox from that of smallpox. Pasteur proposed that the term vaccination be applied to development of immunity to any disease.
VIRUS: The reader of some of the historical documents on this web site might be confused by the term virus as used by writers such as Jenner and Pasteur. The term has changed over several centuries as scientific knowledge of the virus evolved. Included here is a brief exposition on the evolution of the usage of the term virus.
The modern definition of virus, as listed in the Oxford English Dictionary, 2nd ed.(OED): “An infectious organism that is usually submicroscopic, can multiply only inside certain living host cells, (in many cases causing disease) and is now understood to be a non-cellular structure lacking any intrinsic metabolism and a DNA or RNA core inside a protein coat… Formerly referred to a a filterable virus, its first distinguishing characteristic being the ability to pass through filters that retain bacteria.”
The earliest usage cited in OED was for the Year 1527 and referred to a virus as ‘Venom, such as emitted by a poisonous animal.’ By 1728 virus was used in a pathological sense: “A morbid principle or poisonous substance produced in the body as the result of some disease, especially one capable of being introduced into other persons or animals by inoculations or otherwise and of developing the same disease in them.” This was the usage meant by Jenner and others through the majority of the 19th C.
As indicated by OED, by the latter quarter of the Century onward virus took on a more physiological meaning. In 1881 Pasteur wrote, ‘The virus is a microscopical parasite, which may be multiplied by cultivation outside the body of an animal.’ As S.S. Hughes (Virus, p 112, 1977 ) states: “The term ‘virus’ as used by bacteriologists of the 1880s and 21890s meant simply ‘an agent of infectious disease’. This is the usage in Pasteur’s dictum: ‘Every virus is a microbe’ (1890).
The contemporary definition of virus was achieved following the discovery of a filterable, sub-microscopic agent that could infect tobacco leaves, (D.I. Ivanovsky, 1892; M.W. Beijerinck,1898), the existence of the bacteriophage ( F.W. Twort, 1915; F.W. D’Herelle, 1917) and the isolation, crystallization and characterization by Wendell Stanley of tobacco mosaic virus(Science,1935).