Filtrable virus

Pasteur couldn't find the microorganism that caused rabies and suggested a smaller microorganism might be responsible. These viruses were identified: microorganisms smaller than bacteria capable of passing through filters that stop bacteria. This discovery laid the foundational principles for virology.
 Martinus Willem Beijerinck Netherlands 1898 Filtrable virus

Pasteur couldn't find the microorganism that caused rabies and suggested a smaller microorganism might be responsible. These viruses were identified: microorganisms smaller than bacteria capable of passing through filters that stop bacteria. This discovery laid the foundational principles for virology.