The thin red line to separate the sane from the insane?

I don't know how it's presented in it's original form, in the original English version, but in my copy which is in Finnish explains the title of book in 2nd page before the story starts and can be translated:

"Only a thin red line separates the sane from the insane"
- An old Midwest proverb.

I'm curious though, is there an old folksy wisdom such as this in the Midwest, or is it something Jones made up to introduce the concept of "The Thin Red Line" in a different context, than earlier Crimean War/Kipling connection? What do you think?