These days the word ""natural,"" applied with alarming imprecision, puts us on guard, but here it is used appropriately to describe a method of birth control which is attracting substantial interest. Essentially, it's a simple procedure requiring regular inspection of a woman's cervical mucus; this measure, along with temperature changes and other supporting signs (breast tenderness, mittelschmerz, opening of the cervical os), is used to determine the ovulation period. According to enthusiasts, the time involved is minimal--no more than brushing your teeth; the commitment itself is more demanding, as abstinence from intercourse is necessary for 8-14 days a month. Shivanandan explains the procedure carefully, but the major part of her book is devoted to the psychological, emotional, and spiritual ramifications of the method, reports on incomplete research (no success rates have been established), and tentative interpretations of why it works. All agree that abstinence is difficult, although some insist it intensifies intercourse afterwards; many speak of the beauty of sharing responsibility equally; and several offer the kind of comments that leave skeptics laughing (""I had never thought about it, but it is as important as teaching [teenagers] how to make spaghetti, to make them aware of their mucus""). Readers, even those in rapport, will find the book short on absolute facts, stronger on philosophical appeal; and Shivanandan herself, aware of the uniqueness of individual body systems, admits that those interested should seek out a trained counselor. An introduction, then, which may lead sympathetic readers to other sources.