Some writers attribute to climate a great influence in this respect; whilst others regard this view as erroneous, and believe that the differences observed depend rather on racial peculiarities. By advocates of the former view it is assumed that a hot climate leads to the early appearance of menstruation, whilst a cold climate retards the development of this function. Those who dispute the influence of climate bring forward instances of a contrary kind. Thus, among the Samoyede Eskimos, menstruation begins at the age of twelve or thirteen, notwithstanding the fact that they dwell within the Arctic circle; whereas, among the Danes and the Swedes, menstruation begins at about the age of sixteen or seventeen years. Again, we are told that among the Creoles of the Antilles, as in France, menstruation rarely begins before the fourteenth year, whilst in the same islands, girls of African race begin to menstruate, as in Africa, at ten or eleven years of age.[68] These objections to the climatic theory are certainly serious ones. But when we are considering the possible influence of climate upon menstruation, we have to remember that it is possible that climate may exert its influence cumulatively in successive generations, and may not produce its full effect upon the age at which menstruation begins, until after the lapse of several generations. We certainly lack evidence to show that in isolated individuals a change of climate affects the first appearance of menstruation. But it is not impossible that climate may exert such an influence in the course of several generations. Such a view would appear to receive support from our observations on animals, for the sexual life of the latter is notably influenced by the seasons, and change of season resembles in many respects change of climate. In most animals, and more especially in those living in a state of nature, the sexual impulse becomes active at stated intervals only, and these intervals are related to the duration of pregnancy in such a way that the birth of the young occurs always at a season in which the nutritive conditions are favourable. It is widely assumed that even in the human species there remain vestiges of such a periodicity in the sexual impulse. I have discussed this matter very fully elsewhere,[69] and will here do no more than draw attention to the fact that the poetry of spring, which sings partly of love alone, and partly of the relations between love and the annual awakening of nature, bears upon the influence of this season of the year upon the sexual impulse. It seems that the spring also exerts an influence upon the love-sentiments of the child. It is possible that suggestion here plays a certain part, inasmuch as from childhood onwards poetry and many observations teach that there is a connexion between love and the season of spring. Sanford Bell considers that the importance of spring in this connexion depends