What book written by Dr Samuel Howe was quoted in the movie The Miracle Worker starring Anne Bancroft and Patty Duke?

The book quoted in the movie The Miracle Worker is not the direct work of Dr. Samuel Howe. He was a physician, an advocate of the education of the blind and visually impaired, and the husband of Julia Ward Howe, the author of the "Battle Hymn of the Republic".

However, the movie itself is based on a play of the same name written by William Gibson. The play incorporates actual letters written by Dr. Samuel Howe and his wife Julia. These letters recount their experiences in teaching Helen Keller, a young girl who was both blind and deaf, how to communicate and learn.