Final answer:
The Chamberland-Pasteur filter allowed the separation of viral particles from bacteria, facilitating the discovery that viruses, an agent smaller than bacteria, can cause diseases such as tobacco mosaic disease.
Step-by-step explanation:
The development of the porcelain filter, known as the Chamberland-Pasteur filter, was critical in the discovery of viruses. In 1892, Dmitri Ivanowski used this filter to demonstrate that tobacco mosaic disease (TMD) could be transmitted through filtered plant extracts, which had their bacteria removed. This finding indicated that the causative agent was smaller than bacteria, leading eventually to the understanding that a virus was responsible for TMD.
Before this, it was impossible to conclusively determine the presence of infectious agents smaller than bacteria because they could not be seen with light microscopes available at the time. The ability of the Chamberland-Pasteur filter to remove bacteria while allowing something smaller to pass through suggested a new kind of infectious particle, which we now know as viruses. Since viruses are typically smaller than the 0.1 µm pore size of those filters, they could pass through and infect other plants, thereby confirming their filterable nature.