THE STORY OF MENSTRUATION: a 1940 Disney cartoon about periods. A period piece, if you will.
In 1940 Kotex got together with Walt Disney to make a hygiene film, The Story of Menstruation. This 10 minute cartoon was shown to millions upon millions of schoolchildren in the last century, and acted as one of the main educational tools in informing young people about the world of periods.
There's some condescending stuff in there - see the main image for this article on the front page, for instance - but it's pretty solid gynecological information overall. That's because they hired a real gyno to write the thing.
Speaking of writing: some people claim this is the first American film to have the word 'vagina' in the script. It's almost certainly the only Disney cartoon to contain that word.
Disney let the copyright on this gem lapse, so it's in the public domain. Feel free to use this cartoon any way you see fit - it belongs to you, the people.
Thanks to Andrew Clarke.