There is a connection between menstruation and the production of the human ovum. During the first stage of menstruation the mucous membrane lining the uterus swells to twice or thrice its normal thickness, and this growth is a preparation for the reception of the ovum, which, as a rule, is given off by one of the ovaries at this time and passes out into the uterus. Menstruation and ovulation ordinarily occur simultaneously, but they may be independent and take place at different times. If, during this stage, the ovum is impregnated, pregnancy begins, and menstruation ceases until some time after childbirth. In married women conception is more likely to be effected during the first stage of menstruation than during the interval of quiescence; the contrary is almost the exception. Impregnation, however, is likely to occur in the spring more than at other seasons, and this fact coincides with the advent of spring in various latitudes. If the ovum is not impregnated, the material that made the uterine mucous membrane thick during the first week of menstruation degenerates and passes off, constituting the menstrual flow. This stage lasts about five days. A reparative period of about four days follows, and then a period of quiescence until the next menstruation commences. Menstruation is first observed about the fourteenth year, but it may start earlier or later. In general, it comes on {241} earlier in warm climates, and later in the extreme north. The menstruation, too, is likely to show sooner in the labouring classes than in girls who do not work. Even in normal menstruation there is often a marked physiological excitation which affects the entire person. Very commonly a nervous disturbance and sensitiveness are observed, and in women that are not robust there may be mental depression and irritability. The temperature will rise a half degree, and drop to the normal height on the day preceding the flow. There are derangements of menstruation which are symptoms of various diseases. Amenorrhoea is an absence of menstruation in conditions other than pregnancy or lactation. Absolute amenorrhoea is a complete absence of menstruation for several months; relative amenorrhoea is delayed, scant menstruation. Amenorrhoea is common during convalescence from acute diseases; it is also a result of chronic diseases of the liver, stomach, intestines, kidneys, and especially of the lungs; it complicates anaemia, malaria, rheumatism, and other general pathological conditions. Fright, grief, great anxiety, mental shock cause amenorrhoea; so do homesickness and many forms of insanity. There are also local causes of this condition: imperfect development of the uterus or the organs connected therewith, and inflammations of these organs or of the pelvic wall.