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As his career progressed, Rock also became known for his acceptance of birth control. (Birth control was illegal in Massachusetts until the 1965 Supreme Court case "Griswold v. Connecticut".) In the 1930s, he founded a clinic to teach the rhythm method, the only birth control conditionally regarded as moral by the Catholic Church at the time. In 1931, Rock was the only Catholic physician to sign a petition to legalize birth control. In the 1940s, he taught at Harvard Medical School—and included birth control methods in his curriculum. Rock also coauthored a birth control guide for the general reader, titled "Voluntary Parenthood" and published in 1949.