What happened down there?

So NEVER MIND why I was typing these words into Google's ngram tool. But now I'm fascinated. What happened "down there" that peaked in 1881 and dropped off to a low in the late 1920s?

1881: trouble below

Vague theories:

1. Something to do with syphilis, with treatments getting better and better until WHAM penicillin!

2. Lots of medical journals starting around then, and Google Books still dating every issue of some of periodicals to their starting year.