"Its decline in the later decades of the nineteenth century was at one time almost universally attributed to vaccination, but it is doubtful how true this is. Vaccination was never carried out with any degree of completeness, even among infants, and was maintained at a high level for a few decades only. There was therefore always a large proportion of the population unaffected by the vaccination laws. Revaccination affected only a fraction. At present the population is largely entirely unvaccinated. Members of the public health service now flatter themselves that the cessation of such outbreaks as do occur is due to their efforts. But is this so? The history of the rise, the change in age incidence, and the decline of smallpox rather lead to the conclusion that we may here have to do with a natural cycle of disease like plague, and that smallpox is no longer a natural disease for this country."