But conception can also be controlled by avoidance of those parts of the monthly cycle in which conception most commonly takes place. That in the great majority of women there is a time in the monthly cycle when no conception occurs has been noted for a long time. The rough-and-ready method of reckoning the date of birth in relations to the last menstrual period is an example of the assumption that conception will probably have taken place a week later, and the frequency with which such reckoning is justified shows that it is not altogether unfounded. During the war it was possible to make some more exact observations owing to the short leave granted to soldiers to visit their homes. Seigel has published a paper in the "Münchener Medizinische Wochenschrift," 1916, in which he gives information regarding the conception of between two and three hundred children born during the war. He finds that the likelihood of fertilisation increases from the first day of menstruation, reaching the highest point six days later, the fertile period remains almost at the same height till the 12th or 13th day, and then declines gradually until the 22nd day, after which there is absolute sterility. This suggests that conception control can be attained without artificial methods if intercourse is confined to one week in the month. Such control of conception, though natural, does not make it any more desirable to space the births unduly so that the children are brought up in separate units instead of in a happy family group in which they can share games and interests--but it does avoid the risks which are associated with artificial methods of conception control. It is not proposed to discuss in detail artificial methods in this pamphlet, because no advice can be wisely given on this subject in a general way. Those who after careful consideration choose to use artificial means to prevent child-bearing will be wise if they consult their medical attendant as to those methods which are least harmful for their individual case, and ask for careful instruction in their use. Most of the methods so widely advertised are productive of diseased conditions, whether from the nature of the method itself or from the way in which it is used, and all of those recommended to women interfere with normal physiological processes. The object aimed at in methods recommended to women, is either to produce, by drugs or otherwise, conditions in the vagina inimical to the life of the male cell, or to prevent by mechanical means the reception of the semen into the uterus. Owing to the uncertainty in the results of either of the above methods of prevention, the later editions of books which teach conception control now advocate the use of both methods at the same time in order to approximate more closely to certainty of result.