The diversity in the ages at which children menstruate in different countries cannot be laid to any constitutional peculiarities of the races. Observation has established that, when children of the same race and family are brought from a hot to a colder climate, the advent of the first menstruation changes. These girls menstruate not so young as their older sisters, but begin about at the same age as those who are born in the colder climate. In hot countries, for instance in Africa, the negroes and girls in East India begin to have their periods at the age of ten to twelve years. In Sweden and Norway the average age for the first menstruation is sixteen, while further north, in Lapland, the ages vary from eighteen to twenty years. Next in order of importance, influencing the menstrual epoch, are the surroundings and food. In the same climate there are differences in the ages of children that are entirely due to these causes. Children who are pampered and who are nurtured in ease and luxury menstruate earlier than those of the poor or even of the middle class, who are brought up in habits of industry. We observe again a difference in the ages between those who are reared in the country or rural districts and the dwellers in the cities, whether it be in luxurious apartments or in tenement houses. The former grow older and stronger than the latter before the _show_ begins. The temperament also greatly influences the development of the function; children who are nervous, irritable, and of a sanguineous temperament, menstruate earlier than those of sedate habits. The color of the hair and complexion are also indices of the respective appearance of the menses in the _brunette_ and _blonde_. It has been observed that the dark-complexioned girls menstruate sooner under similar conditions than the blondes. Weakly children, who are delicate from some constitutional habit, or whose organism has suffered from disturbances of indigestion or suffered severely from teething in early childhood, menstruate earlier than their stronger and robust sisters. The quantity of the natural menstrual discharge, as well as the time or duration, varies greatly in health with different individuals. We first notice a slimy discharge, which soon becomes tinged with blood, and after one or two days it is almost of pure blood. The flow generally lasts three or four days, very seldom only one day, and sometimes a week to ten days. The monthly recurrence of the menstrual periods averages thirty years; in temperate climates it may overreach this figure a little, while in hot climates it comes much below this average. It does not follow as a rule that because a woman began to menstruate quite young, the change of life will take place earlier. This also depends much upon temperament, habit and mode of life.