Consideration of these facts renders apparent the impossibility of fixing with certainty the date of the beginning of pregnancy, since conception may result from the union of the ovum liberated at the beginning of the period with the spermatozoon introduced at the end of that time; or it may result from the meeting of the male elements already within the oviduct with an ovum discharged a day or two before the occurrence of the menstrual period. The Signs of Pregnancy.-- The cessation of the menstrual period is the sign of the greatest value in women who have been regular; but it must always be remembered that there may be an irregularity of menstruation for the first few months after marriage. The appetite is capricious; morning sickness or nausea in the morning on first getting up is a very common symptom in the early months of pregnancy; enlargement of the abdomen; in the first two months of pregnancy the abdomen is flattened and the umbilicus is depressed; after this the abdomen begins to enlarge. There is also an increase in the size of the breasts, with a deepened color of their areolae and later a watery secretion. The external genitals become swollen and of a bluish color. Feeling of the fetal movements-- that is, the movements of the small parts of the child in the womb-- by the mother is not always reliable, since gas in the intestines has sometimes been mistaken for this. These signs are more valuable when several exist together. The nausea and vomiting of pregnancy, the so-called morning sickness, consists of nausea accompanied often by vomiting or retching of a glairy fiuid, showing itself most frequently on rising in the morning, but sometimes appearing after breakfast. It is aggravated by the assumption of the erect position. It may begin within a few days, but as a rule it does not show itself until the fourth week of pregnancy; and it generally ceases about the fourth month, rarely persisting throughout the entire time. In the majority of cases it does not sensibly impair the health. It is a sympathetic disorder reflected from the uterus; it is aggravated by indigestible food, by sexual excitement, and by emotional disturbances; it is most marked in first pregnancies and in women of highly emotional natures. It is not infrequently due to some inflammation of the uterus or erosion about the external orifice, and disappears on the removal of the cause. Mammary Changes.-- During pregnancy the mammary glands are in immediate sympathy with the growing reproductive organs of the pelvis; consequently a genuine physiologic enlargement commences in these organs from the beginning of gestation. Their glandular structure becomes larger, fuller, and firmer; a sensation of weight or pricking is felt by the patient; the veins become more prominent. The nipples also become enlarged, more elongated, and somewhat erect. Surrounding the nipple is the areola; this becomes darker in color.