This small book deals with the probable conceptive period and its negative phase of two sterile periods, with a consideration of their use in the limitation of the number of pregnancies.
According to Dr. Ogino's theory (for which he states his evidence), the conceptive period is between the twelfth and nineteenth day before the next menses. The sterile periods are from the first to the ninth day, including the first day of the menses, and between the seventeenth and twenty-eighth day in a woman with menstrual periods of the twenty-eight day type. These dates are calculated for each person according to the previous menstrual calendar.
Dr. Ogino points out that some authorities may disagree with him as to the length of life of the sperm, the length of life of the ovum and the psychic influence on the menses-provoked ovulation. He attempts to meet these differences in his little exposition.