It is only by exercise that the faculties are cultivated. It would be very wrong, however, to suppose that each one of them has an individual existence, and by use may be developed separately, and independent of the others. The human faculties seem to have a certain extent of power in common, which they divide in such a manner that one cannot increase except at the expense of the others. An individual who possesses excessive sensibility, rarely enjoys a great degree of muscular vigor. Those men who are noted for muscular strength, are seldom distinguished for the brilliancy of their intellect. Education then acts in two ways: directly, by developing the faculties which it exercises, and indirectly, by opposing the progress of those which it neglects. What it gives to one, it takes from another: it is both a positive, and a negative power. As to the modes of directing it, they act by regulating the use of the three faculties during the period of life when they are forming. This is not the place to say how far education should be carried, so that, in a physical, intellectual, and moral point of view, it should be good: we seek only to determine what it ought to be, in order that a too vivid, or too precocious a facility to receive impressions, may not become the causes of venereal excesses. It is not among the working classes, that those subject to hysteria and hypochondria, are most numerous. The fatigue of body, when constant, dulls the senses. On the other hand, whatever enervates, renders one susceptible to excesses. These facts, which are generally known, and are confirmed by daily observation, ought to show the influence of exercise and rest on the venereal passion. Onanism is arrested in those children, much more readily, who are extremely active and always in exercise, than in those who are sedentary. The period of puberty, this emancipation of the genital organs, is later, by two or three years, in those individuals who take just enough of repose to rest them from fatigue, than in those who take exercise simply because wearied of repose. Other things being equal, the adult who depends upon his daily labor for his bread, thinks less of sexual pleasures than the idler. Helvetius (_de l’homme sect._ 10, _note_ 4,) attributes the lascivious tastes of the Asiatics to their idleness, and the indifference of the Canadians to the pleasures of love, to the fatigues experienced by hunting and fishing. Villermé has attempted to show by statistics the influence of great labor on conceptions, but has not accomplished it. He, however, is disposed to regard the influence of fatigue on the sexual feelings, as the cause of the enormous difference said to have been observed in the Antilles, between the fecundity of the black slaves, and that of the whites. He remembers to have read, that in 1798, at St. Domingo, three marriages of blacks produced only two children, while each union between whites produced three children.