The Katsuragawa family was a Shogunate Oku-ishi (inner physicians, doctors who treated the Tokugawa family) for generations since the sixth Shogun, Ienobu TOKUGAWA and they served as a Hogen (the second highest rank for Buddhist priests) which was the highest rank for surgeons, and therefore they were allowed to read books for Western studies freely.
桂川家は、第6代将軍徳川家宣から代々将軍家に仕える幕府奥医師であり、特に外科の最高の地位である法眼を務め、その為蘭学書を自由に読む事が許されていた。