1. Viruses are highly infectious. Bawden working on the tobacco mosaic virus found it to be infectious even in 1/1000000 dilution.
2. Viruses are highly resistant to acids, alkalies, and salts.
3. Viruses are resistant to high temperatures.
4. Direct sunlight has no effect on viruses.
5. Viruses can be filtered through Brefeld and Chamberlain filters.
6. Viruses can retain the power of infection for long periods, even out of the living cells.
7. Vinson and petre precipitated viruses with the solution of safranin solution, acetone, and ethyl alcohol. The precipitate was obtained by safranin solution. It has no power of infection but it regains it when ethyl alcohol is added to the precipitate.
8. When the cell-sap contaminated with the virus is subjected to a high-speed centrifuge, viruses get sedimented like proteins.
9. Viruses increase in number and size within the living protoplasm of cells.
10. Insects that transmit viruses are known as vectors. A particular virus can be transmitted only by a particular species of insect and one a definite species of host. This sort of selection of the vector and the host is known as physiologic specialization.