The considerations so far brought forward clearly indicate that among primitive races there are frequently one or two seasons in the year--especially spring and autumn--during which sexual intercourse is chiefly or even exclusively carried on, and they further indicate that these primitive customs persist to some extent even in Europe to-day. It would still remain, to determine whether any such influence affects the whole mass of the civilized population and determines the times at which intercourse, or fecundation, most frequently takes place. This question can be most conveniently answered by studying the seasonal variation in the birthrate, calculating back to the time of conception. Wargentin, in Sweden, first called attention to the periodicity of the birthrate in 1767.[151] The matter seems to have attracted little further attention until Quetelet, who instinctively scented unreclaimed fields of statistical investigation, showed that in Belgium and Holland there is a maximum of births in February, and, consequently, of conceptions in May, and a minimum of births about July, with consequent minimum of conceptions in October. Quetelet considered that the spring maximum of conceptions corresponded to an increase of vitality after the winter cold. He pointed out that this sexual climax was better marked in the country than in towns, and accounted for this by the consideration that in the country the winter cold is more keenly felt. Later, Wappäus investigated the matter in various parts of northern and southern Europe as well as in Chile, and found that there was a maximum of conceptions in May and June attributable to season, and in Catholic countries strengthened by customs connected with ecclesiastical seasons. This maximum was, he found, followed by a minimum in September, October, and November, due to gradually increasing exhaustion, and the influence of epidemic diseases, as well as the strain of harvest-work. The minimum is reached in the south earlier than in the north. About November conceptions again become more frequent, and reach the second maximum at about Christmas and New Year. This second maximum is very slightly marked in southern countries, but strongly marked in northern countries (in Sweden the absolute maximum of conceptions is reached in December), and is due, in the opinion of Wappäus, solely to social causes. Villermé reached somewhat similar results. Founding his study on 17,000,000 births, he showed that in France it was in April, May, and June, or from the spring equinox to the summer solstice, and nearer to the solstice than the equinox, that the maximum of fecundations takes place; while the minimum of births is normally in July, but is retarded by a wet and cold summer in such a manner that in August there are scarcely more births than in July, and, on the other hand, a very hot summer, accelerating the minimum of births, causes it to fall in