From David Hartley's Observations on Man, His Frame, His Duty, And His Expectations (1749), I.ii.vi ("To examine how far the Desires of the Sexes towards each other are of a factitious Nature, and deducible from the Theory of these Papers"):
. . . Young Persons hear and read numberless Things, in this degenerate and corrupt State of human Life, which carry nervous Influences of the pleasurable Kind (be they Vibrations, or any other Species of Motion) to the Organs of Generation. . . . It is usual for these Desires, after some time, to fix upon a particular Object, on account of the apprehended Beauty of the Person, or Perfection of the Mind, also from mutual Obligations, or Marks of Affection, from more frequent Intercourses, &c. after which these Desires suggest, and are suggested by, the Idea of the beloved Person, and all its Associates, reciprocally and indefinitely, so as in some Cases to engross the whole Fancy and Mind. . . . The Theory here proposed for explaining the Nature and Growth of these Desires shews in every Step, how watchful every Person, who desires true Chastity and Purity of Heart, ought to be over his Thoughts, his Discourses, his Studies, and his Intercourses with the World in general, and with the other Sex in particular. There is no Security but in Flight, in turning our Minds from all the associated Circumstances, and begetting a new Train of Thoughts and Desires, by an honest, virtuous, religious Attention to the Duty of the Time and Place. To which must be added great Abstinence in Diet, and bodily Labour, if required.