Reading is good for you, that is what your parents and the school has always taught you. There are, however, some books in the world that you will want to avoid at all costs. Recently some Renaissance manuscripts were discovered in a school library that was poisonous. In fact, you could die just by reading them.
As strange as this sounds, some writings on paper can be toxic and they will even be deadly. This is due to the pigments and chemicals used in the ink. The University of Southern Denmark has found when they studied three ultra-rare Renaissance era scripts from their collection. After putting them under the x-ray they found an interesting discovery: glowing green arsenic.
They took the books to their x-ray machine to look at their book bindings, it is well noted that in the 16th and 17th centuries bookmakers used to recycle older parchment to make new books. They hoped they may discover some medieval hidden texts in these Renaissance-era writings.
All three books were caked in a layer of green paint so it was impossible to see with the naked eye, so with their x-ray machine, they hoped to find hidden text in the paint. Unfortunately, they were met with the realization this paint was arsenic. Arsenic is a natural element found all around the Earth, but when it comes in contact with hydrogen and oxygen, it then becomes extremely poisonous. Arsenic poisoning happens primarily by ingestion, therefore reading these pages and licking your fingers could result in death.
Most likely this was not done intentionally, at the time a popular green paint was Paris Green and it was arsenic-based. This was mass produced during Victorian times, many museums today contain paintings that are poisonous. The undercoat in these books was probably used to kill insects and vermin, keeping the books safe from pests.