Villermé proposed to establish, from the register of births, the periods of the year when conceptions occur most frequently. He arranged the months in the following order. May, June, April, July, February, March, December, January, August, November, September, October. Hence the three months when there are the most conceptions are April May and June, and those in which there are the fewest are September, October, and November. Hence it is in spring, at that period of the year when vegetation sprouts forth and when the trees are covered with foliage, when most animals seek their mates, that pregnancy is most common: while in autumn, that season in which vegetable life is as it were extinguished, is also the period when the human race labors least at reproduction. The results obtained by Quetelet and Smits, conform entirely with the above. It now remains to know whether the difference between spring and autumn arises from there being less procreative exertion or whether conception or impregnation at that time are more easy. To resolve this question Villermé consulted the criminal calendar to ascertain at what period of the year there were the most attempts at rape: and he found that it was the same as that when the most conceptions occur, that is in the spring. The same result was obtained by Quetelet and Smits. May not these crimes be more common in the spring because then men have more opportunity of being guilty, as at that time females may be found alone and loosely clothed, in the woods and distant places? But these same circumstances exist in the months of August and September, and yet the respective number of these crimes diminishes in these two months. Nor can this greater number of pregnancies be attributed to the fact that more marriages are contracted at one period of the year than at another, for the _maximum_ and _minimum_ of births can be referred in every country and at all times, with but few limitations to the same periods, while the _maximum_ and _minimum_ of marriages in different countries present great and numerous differences. We may then consider it as determined that man is subject to a certain extent to a kind of _periodical heat_, which returns every year in the spring.