Since 1852, several conferences were held involving European powers, with a view to uniform action in keeping out the infection from the East and preventing its spread within Europe. All but that of 1897 were concerned with cholera. No result came of those at Paris (1852), Constantinople (1866), Vienna (1874), and Rome (1885), but each of the doctrine of the subsequent one of constructive infection of a ship as coming from a scheduled port, and an approximation to the principles advocated by Great Britain for many years. The principal countries which retained the old system at the time were Spain, Portugal, Turkey, Greece, and Russia (the British possessions at the time, Gibraltar, Malta, and Cyprus, being under the same influence). The aim of each international sanitary convention had been to bind the governments to a uniform minimum of preventive action, with further restrictions permissible to individual countries. The minimum specified by international conventions was very nearly the same as the British practice, which had been in turn adapted to continental opinion in the matter of the importation of rags.