So I'm messing around with Google Ngrams, which looks at usage of specific words in books. I think the data is compiled with all the captchas we've been filling out for years.
Anyways, I type in the terms, "anus," "sphincter," and "butthole" and there's a sharp decrease in the usage of all 3 of these terms beginning in 1910 and bottoming out in 1926. I used the term "toe" as a control, and you can see that it does not follow the same pattern.
Data: http://i.imgur.com/5E2KRft.png
Now, I was going to post this to /r/shittyaskscience but I'm actually interested in what the real answer might be. Let me know if this isn't the right place for this question.
For words as uncommon as "sphincter," Google Ngram is not particularly useful before ~1940. Due to the exponential increase of material both produced and available to Google, the data does not represent the pure number of times the words are used, but what percentage of the corpus they constitute. The graphs for words with low usage are inherently too messy to be worth much inquiry. It'd be better to interpret that as an anomalous spike between 1860 and 1920, not a drop off afterwards.
