It’s hard to believe, but the word clitoris did not appear in Playboy magazine until 1968, in an interview with Masters and Johnson, the famous sex researchers.

Two years earlier, the pair had published “Human Sexual Response,” their first book, based on more than 10 years of clinical research. It was a best seller, and it rattled the culture in much the same way the first Kinsey Report had in 1948.

Alfred Kinsey compiled his information from surveys. His work was sociology. William Masters and Virginia Johnson actually watched people  a lot of people  have sex, with heart monitors and other gizmos attached to their subjects’ bodies. Here was science. Here was raw data that steamed America’s frozen peas.

“Human Sexual Response” wasn’t easy or especially titillating reading, Thomas Maier points out in his new book, “Masters of Sex: The Life and Times of William Masters and Virginia Johnson, the Couple Who Taught America How to Love.” Masters and Johnson wanted their work to be taken seriously, and wanted to stay a step ahead of the morality police, so they tended to write in almost comically dense medicalese.