Over the course of the nineteenth century, American women began having fewer and fewer children.

This change owes a lot to doctors like Charles Knowlton, born on this day in 1800. Knowlton was an American doctor and philosopher known for his unconventional views. He was also one of the first members of the medical establishment to write openly about birth control methods and human sexuality. Even though the innocently named Fruits of Philosophy, his pamphlet first published in 1832, had negative consequences for him personally, some historians believe that the pamphlet and subsequent reprintings in America and England helped to change the conversation about birth control.

“A demographic revolution took place in the United States between 1800 and 1940,” writes historian James Reed. “The high birth rates and high mortality characteristic of a premodern society were replaced by a new vital economy of fewer births and fewer deaths.”

Knowlton, like other physicians of this period, saw how sex could, and frequently did, lead to death. Women regularly died of “puerperal fever,” or post-partum infections, and other ailments associated with childbearing. In fact, write Emily Baumrin, Billy Corbett and Amita Kulkarni for Dartmouth Medicine, “puerperal fever was far and away the most common cause of maternal mortality and was second only to tuberculosis among all causes of death for women of childbearing age.” And children regularly died in their first year of life.

Fruits is widely credited with helping to popularize ideas about birth control as a medical intervention.

It discusses various methods of birth control, ultimately concluding that an injection of a sort of primitive (by modern day standards) spermicide was the best option. In other words, a vaginal douche.

The pamphlet also put forth ideas on population that wouldn’t be popularly accepted for many years to come. In fact, at the beginning of the text, Knowlton wrote that “the time will come when the earth cannot support its inhabitants,” and that birth should be restrained to prevent the “inconceivable amount of human misery” that could be the result of overpopulation.

But Knowlton clearly didn’t just write about theory. Fruits was a practical guide to contraception that acknowledged that people wanted to have sex, and not just for the purposes of bearing children. “Surely no instinct commands a greater proportion of our thoughts or has a greater influence upon happiness, for better or for worse,” he wrote.

This pragmatic attitude didn’t go over so well with authorities. After the book was published, writes Reed, Knowlton was fined fifty dollars and prosecuted on three separate occasions “under the Massachusetts common law obscenity statute.” But although he served three months hard labor as the result of one of these legal suits, Reed writes that his reputation in the community was solidified by Fruits.

“According to Knowlton’s account of the trial,” Reed writes, “one juror tried to console him” for his plight. “Well, we brought you in guilty,” the juror said. “We did not see how we could well get rid of it, still I like your book, and you must let me have one of them.” The judge in the case requested a copy as well, Reed writes, “and the prosecuting attorney returned his share of the costs to Knowlton.”

Later in his career, Knowlton helped figure out what caused puerperal fever, write Baumrin, Cobett and Kulkarni, advancing women's health. As well, his book lived on. It was reprinted in the United States and in Britain, where it was at the heart of a famous obscenity trial that promoted the discussion of birth control in Britain.