Virus
Collier's New Encyclopedia (1921)
a term used in medicine to designate the materies morbi of zymotic diseases. It more specially designates those peculiar poisonous matters which can reproduce themselves under favoring conditions to an endless degree. The poison of the cobra is a specific virus which, when introduced into the human system, acts as a most virulent poison; but the poison is not multiplied within the human subject, and one person affected by the poison cannot communicate the disease to another. In like manner, morbid products from decaying vegetables under certain conditions of heat and moisture may possibly originate the virus of malarial fever; but the virus is not propagated within the human organism, or, at all events, never in such a form as to render it capable of producing the same disease in others. By some the virus of the contagious or infectious diseases is supposed to be a contagium vivum seu animatum, the theory being that the virus consists of living beings or low organisms. Such views have been advocated by Kircher, Lancisi, Vallisneri, mur, Linné, né, Henle, Roberts, and Reaumur, others; and although the theory of a contagium vivum is not as yet complete, the discussion of it is the most important which has ever engaged the attention of The most prominent medical men. characteristic of each specific virus is that it can reproduce itself within the human organism, and to an unlimited extent, each virus preserving its own specificness. Experience and observation tend to confirm the hypothesis that each specific disease breeds true, though, in the course of 1,000 years, it is possible that the changes within certain limits may take place, as is the case in animals and plants. The natural conclusion follows that diseases of this class do not originate spontaneously, but are propagated each from its own kind, though some contend that they do not originate, even in our own day, spontaneously or autochthonously. Another remarkable peculiarity belonging to many, but not to all, diseases propagated by a specific virus, is that a single attack of the disease successfully surmounted produces absolute or relative immunity for a certain length of time, or even for the remainder of life. See BACTERIA.
What Has Changed in the Last Century
When Collier's wrote this in 1921 "virus" still meant almost any self-multiplying "poisonous matter," broad enough to cover cobra venom and the supposed miasma of malaria, and the question of whether contagion was a living thing (contagium vivum) was called "the most important discussion which has ever engaged" medical men. That question was settled decisively: viruses are now known to be particles of DNA or RNA in a protein coat, too small to be filtered out or seen in a light microscope. Wendell Stanley crystallised tobacco mosaic virus in 1935 and the electron microscope made viruses visible from the late 1930s, while malaria was shown to be caused by a protozoan parasite spread by mosquitoes, not a virus at all. Virology since has produced polio vaccines, the global eradication of smallpox declared in 1980, the identification of HIV in 1983, and the mRNA vaccines made against SARS-CoV-2 in 2020.
Written for this edition, 2026.