When you are citing something you found on a website, the website itself should be considered the container no matter the original form of publication. However, you can give details about the original publication in your prose or supply the original publication information in the optional-element slot, at the end of the entry in the works-cited list. 

The following sentence and the entry in the works-cited list below provide an example:

Adherents of the eugenics movement in the early twentieth century believed that forced sterilization should be legal because it was “a safeguard to society” (“Aiding Defectives”).

Work Cited

“Aiding Defectives.” Vermont Eugenics: A Documentary History, www.uvm.edu/~eugenics/primarydocs/onbfpst032031.xml. Originally published in The Burlington Free Press, 20 Mar. 1931.