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L'Onanisme, an essay on masturbation written by Dr. Tissot, is of particular historical interest because it serves as a reminder of the origins of the repression of sexuality. To better understand Dr. Tissot's rationale for condemning masturbation, an anlaysis of the essay was carried out and revealed that the primary concern was the prevention of depopulation and degeneration. Ultimately, this led to a new line of thought in sexology - the ³prophylactic² approach.