1. Survival of variola virus in raw cotton;MacCallum;Bull WHO,1957
2. Effect of temperatures of up to 45°C on survival of variola virus in human material in relation to laboratory diagnosis;MacCallum;Bull WHO,1957
3. Survival of variola virus in dried exudate and crusts from smallpox patients;Downie;Lancet,1947
4. Survival of smallpox virus (variola minor) in natural circumstances;Wolff;Bull WHO,1968
5. Palaeontology of smallpox;Zuckerman;Lancet,1984