US National Archives
Nara: American Originals: Letter From Upton Sinlcair to President Roosevelt
Click here to see an original page of a letter from Upton Sinclair to President Roosevelt regarding the conditions of meat-packing plants.
US National Archives
Nara: American Originals: Meat Packing House Inspections
Check out this National Archives and Records Administration site for a short explanation of the term "muckraker," and for a quote by Sinclair, whose writings influenced the passage of the Meat Inspection Act in 1907.