In a study exemplifying both brevity in experimental design and brilliance in execution, Fenner1 delineated the pathogenesis of the acute exanthems. He lumped together the human diseases of smallpox, chickenpox, measles, and rubella because of similarities in clinical presentation after a relatively long incubation period, even though etiologically these diseases are caused by a diverse group of DNA and RNA viruses (poxvirus, herpesvirus, paramyxovirus, and togavirus, respectively). The animal model that he selected was the murine virus infection called mousepox or infectious ectromelia. Inasmuch as the natural route of infection is through minute abrasions in the skin, Fenner inoculated the test animals in either the foot or pinna with small doses of mousepox.