How would a medieval doctor identify a poison that was administered through a cut? Is it strictly by symptoms? If the implement is produced, would that help in identifying the poison?
The story is fantasy, but I've tried to stick closely with historical and medical facts from medieval times--14th to 15th century. The doctor is a soldier with training in medicine. The government has been allowing medical experimentation and study to an extent, so he is experienced and learned for my purposes, but limited by lack of scientific and medical technology.
Also, implement is a dagger, and yes it can be provided. Poison is a combination of plant, venom, and minerals, so symptoms would be difficult to diagnose.