Unearthed during a moth-proofing session from my family's old storehouse. The details of its origin are unknown, but I believe it's from the late Edo period. "On'ekiron Kaigen" --AI Explanation Below-- About the original work: "On'ekiron" (瘟疫論), is a medical book written by **Wu Youxing (呉有性)**, a Chinese physician of the late Ming and early Qing dynasties. It is believed to have been completed in 1642 (Chongzhen Renwu). Content: It discusses the epidemic diseases (infectious diseases) prevalent at the time, and established the foundation for a groundbreaking theory of febrile disease, attributing the cause to a pathogen called "Reiki" (戻気). Nature of "On'ekiron Kaigen": From the word "Kaigen," it is considered to be a commentary, explanatory book, or an excerpt of the original "On'ekiron." Influence on Japan: "On'ekiron" was introduced to Japan during the Edo period, and many Wakokubon (Japanese-style printed books) were published, greatly influencing the Japanese medical world, especially the development of febrile disease studies. The "On'ekiron Kaigen" in this image is likely a Wakokubon published in Japan after the Edo period, or a copy or original version brought from China. Judging from its condition, it is presumed to be quite old. Condition: The book itself shows signs of aging, with paper tears, stains, and insect damage. Thank you for viewing.