It is so much easier for the popular mind to regard any act performed by an individual or by one sex as exclusively affecting one particular individual or sex engaged in its performance that it is extremely difficult for most persons to fix their minds steadily upon the inseparable double character of this exceptional human act. It requires a certain amount of generalizing power to do this; and the power of generalization, which leads to the recognition of abstract truth and to the perception that a true principle is of far higher value than any number of phenomena, is an advanced attainment of human beings. Abstract truth commonly seems vague as compared with a material fact. We are also so accustomed in using all our other senses, sight, hearing, etc., to regard them as individual possessions, that it is difficult to separate the sexual sense from all others. Yet it distinctly belongs to a different class from all our other senses, because its ultimate expression is not a simple individual performance, but is a social act of vital importance to the race. The imperfection of our intelligence, which makes it easier to consider a joint act in its diversity than in its unity, has led to very imperfect observation of physiological facts and many false deductions from such imperfect observation. Very grave social errors, leading even to the general debasement and ultimate destruction of national life, flow from the hitherto rudimentary condition of our human intelligence in relation to the sexual powers. Fornication is the promiscuous intercourse of the sexes. It is the yielding to the domination of the simple physical impulse of sex, with no perception or acceptance of the mutual responsibility involved in the relation, and with no regard to a fundamental aspect of this relation--viz., the well-being of offspring. Fornication is the attempt to divorce the moral and physical elements of human nature, and to ignore the inseparable results of joint action. In considering this subject from a medical point of view, we are at once brought face to face with a conflict nineteen hundred years old. Christianity, springing up when the Roman Empire was perishing through its vices, stamped fornication as the gravest of social crimes. There is nothing more strongly marked in the earlier records of this religion than the stern, even awful, condemnation of whore-mongers. The sin of sexual impurity is denounced as the essence of hatred and fraud. We observe that wherever the Christian Church becomes hypocritical and cowardly, and fails to reprobate this sin alike in men and women, in high and low, in the State and in the family, or fails to be the leader of the people against organized evil, there the Christian Church begins to fall into contempt, and the _vox populi_ condemns it.