Thomson, Discourse, 1750 (C4r)

The authorizing citations have moved from being printed in the outer margins on the side of the page to the bottom of the page, a practice we would describe as footnotes.

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Adam Thomson, A discourse on the preparation of the body for the small-pox, and the manner of receiving the infection. Philadelphia: Benjamin Franklin and David Hall, 1750. (sig. C4r)

University of Pennsylvania, Curtis 455 (public domain)