/kloc-at the end of 0/9, people discovered the virus again. Before this, people have invented a filter that can block the passage of bacteria when studying microorganisms, and used this filter to remove bacteria from liquid. However, in 1892, a Russian plant physiologist named ivanovski (1864 ~ 1920) found that the diseased tobacco juice could still make good leaves sick even after being filtered by a filter. He deduced from this that there must be smaller microorganisms that can pass through the bacterial filter. Later, when some doctors were studying some diseases of people and animals, they also found that some filtered liquids with bacteria removed can still make people and animals sick. At that time, people didn't have a "smart enough" observation method, so they couldn't see what this small microorganism smaller than bacteria looked like, and they couldn't be stopped by filters. However, from the results of their activities, they inferred the existence of this filter-strong, pathogenic microorganism and gave it a name, called "virus".

The discovery of this virus marks a great step forward in human understanding of microorganisms. However, because it is so small, it took decades after it was discovered, and it was not until the 1940s that people really saw it clearly with the newly invented electron microscope.