Beijing

古有種痘一法起自江右達於京畿究其所源云自宋真宗時峨眉山有神人出為丞相王旦之子種痘而愈遂傳於世其説雖似渺茫然以理揆之實有參贊化育之功因時制宜之妙盖正痘感於得病之後而種痘則施於未病之先正痘治於成病之時而種痘則調於無病之日自表傳裏由裏達表既無諸證夾雜於其中復有善方引導於其外薫蒸漸染胎毒盡出又何慮乎為患多端變更莫測以致良工束手於無可如何之地耶此誠去險履平避危就安之良法也

In the past there was a method of planting smallpox. It began in Jiangyou and spread to the capital region. As for where it came from, people tell a story from the time of Emperor Zhenzong of the Song. A holy man came out of Mount Emei and planted smallpox in the son of the chancellor Wang Dan, and the boy recovered. From then on it was handed down in the world. The story may seem far-fetched. But judged by reason, the method truly helps [Heaven and Earth] in their work of creating and nourishing life, and it wisely suits the treatment to the time. Natural smallpox is caught after one falls ill, but planted smallpox is given before any illness. Natural smallpox is treated when the illness has already taken hold, but planted smallpox is managed on a day when the child is well. [The seed's qi] passes inward from the surface, and [the poison] comes back out from inside to the surface. No other illnesses are mixed in, and good prescriptions guide it from outside. Steamed out little by little, the fetal poison comes out completely. Then why fear harm of many kinds and changes no one can foresee, which leave good doctors helpless? This is truly a fine method for leaving danger behind and walking on level ground, for avoiding peril and reaching safety.