Having to repeat oneself, for what cause one is unsure...
...That the permitting this Air to escape and mix with the Atmosphere, is usually offensive to the Company, from the fetid Smell that accompanies it.
That all well-bred People therefore, to avoid giving such Offence, forcibly restrain the Efforts of Nature to discharge that Wind.
That so retain’d contrary to Nature, it not only gives frequently great present Pain, but occasions future Diseases, such as habitual Cholics, Ruptures, Tympanies, &c. often destructive of the Constitution, & sometimes of Life itself...
http://teachingamericanhistory.org/library/document/to-the-royal-academy-of-farting/