THE PROBABLE SIGNS.--Obviously, phenomena for which the child is responsible--such as have just been described--supply the most trustworthy evidence of pregnancy; and these phenomena alone are accepted as positive signs. But there are earlier manifestations which intimate very strongly that conception has taken place. Shortly after pregnancy has become established changes begin in the uterus, as physicians call the womb, and soon reach the point where they may be recognized by a simple examination which enables the physician to express an opinion little less than positive. As one result of pregnancy, for example, the supply of blood is increased to all the organs concerned with the reproductive process. Partly on account of this congestion and partly on account of embryonic development, the uterus becomes altered in a number of ways. Although these changes occur regularly in pregnancy, they may also occur when the womb is enlarged from other causes; therefore, if a physician should make the diagnosis of pregnancy whenever they were found, he would make it somewhat too frequently. With a little patience, however, he excludes the chance of being misled; a second examination, approximately four weeks after the first, will generally place the existence of pregnancy beyond question, for under normal conditions the degree of enlargement which takes place in a pregnant womb during a given interval is absolutely characteristic. THE PRESUMPTIVE SIGNS.--Although women are most often led to suspect that they are pregnant by symptoms which are of such doubtful significance that they must be regarded as merely presumptive evidence, the practical value of these symptoms is attested by the fact that subsequent developments rarely fail to confirm the suspicion. Perhaps they prove misleading once or twice in a hundred cases; the number of mistakes is small, because the diagnosis is commonly made not from only one of these doubtful signs but from a group of them. In order of importance the doubtful or presumptive signs of pregnancy are these: (1) cessation of menstruation, (2) changes in the breasts, (3) morning sickness, (4) disturbances in urination. _The Cessation of Menstruation_.--The failure of menstruation to appear when it is expected is nearly always the first symptom of pregnancy to attract attention, and, as a rule, when this happens to healthy women during the child-bearing period--which usually extends from the fifteenth to the forty-fifth year--it may be taken to indicate that conception has occurred. But there are exceptions to this very good rule. Besides pregnancy we are acquainted with several conditions that cause temporary suppression of menstruation; and to understand its significance we must learn something of the menstrual process itself.