 At the time, Negri mistakenly described the pathological agent of rabies as a parasitic protozoa.A few months later, Paul Remlinger (1871–1964) at the Constantinople Imperial Bacteriology Institute correctly demonstrated that the aetiological agent of rabies was not a protozoan, but a filterable virus.Negri went on, however, to demonstrate in 1906 that the smallpox vaccine, then known as "vaccine virus", or "variola vaccinae", was also a filterable virus.