On the System or Theory of Pharmacology

An old textbook found in a ruined house, pointing to an old secret that has repercussions today.

ON THE SYSTEM

or Theory of Pharmacology

or, a Treatise

concerning the Principles

of the

New Elements of Medicinal Preparations

The book describes a wide number of medicines for all sorts of ailments.  Some make use of astrological theories, but most have a basis in some kind of medical knowledge.

There are a number of handwritten notes in the margins, but enciphered in some way to protect their secrets.  Dangerous poisons?  Private memoirs?  Secret confessions?

A folded-up page is tucked in the book, an old single broadsheet newspaper that's been folded and unfolded many times.  The main article is about someone famous at the time being poisoned.  It's not clear from the article whether the poison killed them or not.

The book and the newspaper were published within a year of each other in the same city, a decade or so after the apocalypse.  There's a chance the author might still be alive today.

After forty years or so, how could the secret in the margins still matter now?