DO YOU KNOW

How were viruses discovered?

     Tobacco mosaic is a disease that infects several species of plants. In the 1890s, Dmitri Ivanovski, a Russian scientist trying to identify the bacteria that caused the disease, collected the sap of infected plants and passed the sap through porcelain filters that could trap the smallest of bacteria. Not a single bacterium was trapped in the filters even after repeated attempts. Yet the filtered sap could infect healthy plants. Ivanovski concluded that his filters were defective and left it at that.

     Some years later, a Dutch botanist, Martinus Beijerinck, repeated the Russian’s experiment and came to the conclusion that there was nothing wrong with the filters but that the infectious agent was tinier than any bacteria known and was passing through the filters. He dubbed it a ‘filterable virus’, virus being the Latin word for poison.

    Soon afterwards a German scientist found that the infectious agent causing foot-and mouth disease in cattle was also a filterable virus, and not a bacterium.

     In 1901, the infective agent causing yellow fever was also found to be a filterable virus. Thus scientists became aware of a new type of infectious agent, different from bacteria, and in course of time, the term ‘filterable virus’ was shortened to just ‘virus’.

     In 1914, a German scientist demonstrated that the common cold was caused by a virus, yet even in 1918 when the Spanish Flu caught the world by its throat, physicians clung to the notion that the disease was caused by some sort of bacteria.

    Another decade and more was to pass before the electron microscope was invented and man finally got to see one of his greatest enemies — the virus.

     The electron microscope was invented in the 1930s.