Isserlin (1835–1911), a lumber merchant originally from Slutsk, had settled in Prostken in the 1860s. His eldest son, Jonas Isserlin, was a merchant in Königsberg; his youngest son, Marcus Max (born 1874), studied medicine at the Albertina and became a well-known balneologist. An obituary in the newspaper “Israelit” dated October 19, 1911, praised Isser Josua Isserlin’s piety and his descent from a “highly respected Jewish family”: “His—one might almost say excessive—honesty in business was almost proverbial on the Russian border; he resided in Prostken in East Prussia. …