While half of this page is cut off, it’s possible to get a rough idea of what it’s banging on about. We already know the chapter is about dragonglass and its uses – the opposite page is where Sam gets the epiphany about mining for dragonglass on Dragonstone.
The passage seems to talk about tales of dragonglass being used as a possible cure for illness and disease when it is ingested. It then proceeds to say that while little harm occurs from the ingestion, that you “can’t discount the harm to the gullible”. It’s fair to say the writer of the book is not convinced, but surely this little tidbit will be enough to convince Sam and Jorah to give it a try. They don’t have much to lose at this point.