In 1832, Knowlton moved his family and medical practice to
Ashfield, Massachusetts. A year later, the town's new minister, Mason Grosvenor, began a campaign against "infidelity and licentiousness", targeting Knowlton as its source. Knowlton had written a little book entitled,
The Fruits of Philosophy, or the Private Companion of Young Married People, and had been showing it to his patients. It contained a summary of what was then known about the physiology of conception, listed a number of methods to treat infertility and impotence, and explained a method of
birth control he had developed: to wash out the vagina after intercourse with certain chemical solutions. Knowlton was prosecuted and fined in Taunton, Massachusetts for the book.
Abner Kneeland printed a second edition of
Fruits of Philosophy in Boston in 1832, allowing it a wider circulation than the few closely guarded copies Knowlton had been lending to patients. This led to Knowlton's imprisonment in Cambridge at "hard labor" for three months, and was a central issue in Kneeland's blasphemy trial in 1838. Reverend Grosvenor filed a complaint against Knowlton in Franklin County, but after two juries failed to convict him, the charges were dropped. Grosvenor left Ashfield, and became a general agent for the
Aetna insurance company. ==Later life==