On 9 Apr 1995, Keith Sturts wrote:
> Had human cognition already gained a good sense of the existance of the
> viruses and their nature before the use of the electron microscope to
> actually see them physically in about 1931?
>> Or were the existence of the viruses and the pathology of their
> activities a medical mystery until the electron microscope.
>>> Thanks for any response you can ive
I hope these dates and keywords will help you in your search
(I believe the first EM studies appeared around 1940)
Viruses were distinguished from bacteria as the causal agents of
plant and human diseases by passing them through filters that would
retain bacteria, and were referred to as 'filterable "agents"'.
Discovery of TMV (tobacco mosaic virus) by Beijerinck and Ivanovski.
Reed and Carroll (yellow fever virus)
1917 discovery of bacteriophages (d'Herrell)
in the 1930s Luria and Delbrueck: genetic (quantitative) studies
with bacteriophages and bacteria (plaque assays).
1935 TMV (tobacco mosaic virus) was crystallized, and chemical
components (protein/ribonucleic acid) analyzed.