PERIODICITY.
The periodicity of this function is remarkable. With those who are regular, menstruation occurs every twenty-eight or twenty-nine days, or once a lunar month. There is, however, considerable variation from this rule. Some having menstruation twice a year appear to enjoy very good health. Some have asserted that the frequency of menstruation varies considerably according to climate. Linnæus, it seems, saw women in Lapland who menstruated about once a year. Dr. Denman speaks of the inhabitants of Lapland, where women do not menstruate till they arrive at mature age, and then only in small quantities and at long intervals, and sometimes only in summer. But if they do not menstruate according to the genius of their country, it is said they suffer equal inconvenience, as in warmer climates, where the quantity discharged is much greater and the period shorter.