The Discovery of Viruses 1892 – Living Microbes

The science journalist Robert Adler wrote: 

“The list of diseases caused by viruses—rabies, smallpox, yellow fever, polio, influenza and AIDS—reads like a catalog of human suffering. The scientists who unlocked the secrets of viruses were literally feeling their way in the dark, trying to understand something they had never even imagined before.”

Viruses occupy a strange space between the living and the nonliving. They do not possess all the molecular equipment needed to reproduce themselves. But when they infect animals, plants, fungi or bacteria, they can use their hosts to produce countless (trillions of) viral copies. Some viruses can drive host cells into uncontrolled proliferation, which can lead to cancer (for example, HPV). 

Today, it is clear that most viruses, being about one-hundredth the size of an average bacterium, cannot be seen with an ordinary light microscope. Virions (virus particles) consist of genetic material in the form of DNA or RNA and an outer protein coat. Some viruses may also have a lipid envelope (small organic molecules) when outside the host cell.

• In 1892, the Russian biologist Dimitri Ivanovsky took one step toward understanding the cause of tobacco mosaic disease. While investigating this disease, which destroyed tobacco leaves, he filtered extract from crushed diseased leaves through a fine porcelain filter designed to trap bacteria. Surprisingly, the liquid that passed through the filter was still infectious. Ivanovsky never understood the true viral cause, however, because he believed that toxins or bacterial spores might be the causative agents.
• In 1898, the Dutch microbiologist Martinus Beijerinck performed a similar experiment. Believing the new infectious agent to be liquid in nature, he called it “soluble living germs”. 
• Later researchers were able to grow viruses in media containing guinea-pig corneal tissue or fertilized chicken eggs. 
• Viruses became visible only in the 1930s, with the electron microscope.

About the Article Image: Most animal viruses have a symmetrical, nearly spherical shape. Viruses are generally much smaller than bacteria.

Historical Figures Mentioned in the Article: Martinus Willem Beijerinck (1851–1931), Dimitri Iosifovich Ivanovsky (1864–1920)

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