Dissertation Thread 2013-2014

Just wondering on which reference you guys would use here


I'm writing about a certain disease and want say 'X was the first person to reference this disease.(Reference).

Now my two sources for this is an article in a journal talking about the history of the disease and it references X's original work in French with the exact page.

Do I reference the journal article on the history of the disease or X's original manuscript which is from the 18th century and in French?