Just Like a Pearl - S0.E6

While searching for a knife to cut a cake, Pinoko finds a case containing a scalpel encased in stone. Jack tells her the story of how he received it from Dr Jotaro Honma, who saved his life and inspired him to become a doctor. Years ago, in the operation which saved Jack's life, Honma accidentally left a scalpel inside Jack's body. During a second surgery, Honma extracted a stick from Jack's body which had secreted calcium to encase the scalpel, like how an oyster creates a pearl. Honma referred to it as a "miracle of life", but questioned if someone should have control over another human's life. Years later, the ageing Honma slipped into unconsciousness with cerebral softening/hemorrhage. Jack operated but could not save Honma and blamed himself for his death. In the present, Jack visits Honma's grave and considers his comment, which he thinks would make it pointless being a doctor. Back on the cape, Black Jack throws the scalpel into the ocean, proclaiming that he is a doctor.