Original Seven Barks pamphlets, published in the late 1800s and now in the public domain, featuring testimonials including this one from May 8, 1881:

Dear Sir:-Your medicine is the best I ever saw, all here who have used it speak in the highest favor of it. I could give you any amount of names who will testify to its virtues. Your friend, J. H. CARPENTER, Washington, Warren Co., N.J.