He used porcelain filters whose pores inhibited bacterial passage, but allowed passage of plaques. He thought something was wrong with his filter, but he published anyway, and others repeated his experiment hoping to disprove his findings. He and others proved that smaller units, viruses, passed through the filters. Because he was able to force a virus into a crystalline structure, he thought it could not be alive. When he rehydrated the crystals, they functioned normally.
Virus have symmetrical shapes.
A good example of this is the adenovirus, an icosohedron made of equilateral triangle subunits. This provides two-fold rotational symmetry. The introduction of European rabbits into Australia generated an interesting study in virus evolution. Rabbits were introduced to Australia to give hunters something to shoot. But, they multiplied so fast that they competed with the sheep for the available grass.