In 1898, E. Nocard from the Alfort National Veterinary School and his colleagues from the Pasteur Institute have succeeded in growing the bovine pleuro-pneumonia agent, using small bags of collodion inserted into the peritoneum of rabbits. Unfortunately, the cultured micro-organism was considered by us as a filterable virus. The confusion between true viruses and mycoplasmas has persisted for a long time and delayed the development of the modern concept of virus until the 1940's.