Let us begin with some considerations of importance with regard to the critical stage under discussion. The change from childhood to puberty is not so clearly determined by nature but that it varies according to individual temperament and racial conditions. Everybody knows the differences which have been observed with regard to this between hot and cold countries, and every one sees that ardent temperaments mature earlier than others; but we may be mistaken as to the causes, and we may often attribute to physical causes what is really due to moral: this is one of the commonest errors in the philosophy of our times. The teaching of nature comes slowly; man's lessons are mostly premature. In the former case, the senses kindle the imagination, in the latter the imagination kindles the senses; it gives them a precocious activity which cannot fail to enervate the individual and, in the long run, the race. It is a more general and more trustworthy fact than that of climatic influences, that puberty and sexual power is always more precocious among educated and civilised races, than among the ignorant and barbarous. [Footnote: "In towns," says M. Buffon, "and among the well-to-do classes, children accustomed to plentiful and nourishing food sooner reach this state; in the country and among the poor, children are more backward, because of their poor and scanty food." I admit the fact but not the explanation, for in the districts where the food of the villagers is plentiful and good, as in the Valais and even in some of the mountain districts of Italy, such as Friuli, the age of puberty for both sexes is quite as much later than in the heart of the towns, where, in order to gratify their vanity, people are often extremely parsimonious in the matter of food, and where most people, in the words of the proverb, have a velvet coat and an empty belly. It is astonishing to find in these mountainous regions big lads as strong as a man with shrill voices and smooth chins, and tall girls, well developed in other respects, without any trace of the periodic functions of their sex. This difference is, in my opinion, solely due to the fact that in the simplicity of their manners the imagination remains calm and peaceful, and does not stir the blood till much later, and thus their temperament is much less precocious.] Children are preternaturally quick to discern immoral habits under the cloak of decency with which they are concealed. The prim speech imposed upon them, the lessons in good behaviour, the veil of mystery you profess to hang before their eyes, serve but to stimulate their curiosity. It is plain, from the way you set about it, that they are meant to learn what you profess to conceal; and of all you teach them this is most quickly assimilated.