In the first place, the difference between hereditary and acquired sexual anomalies is only relative and gradual, so that it is necessary to avoid opposing one against the other. When an anomaly arrives spontaneously in the first sexual glimmer of the child's mind during its development, it is obvious that it is the expression of a profound hereditary taint, the result of blastophthoria or of unfortunate combinations of ancestral energies which have been associated by the conjugation of the two procreative germs. In such a case it is comparatively easy to prove that this is a pathological symptom independent of the will of the individual. But a continuous series of degrees in the intensity of a hereditary predisposition to a certain sexual anomaly, or to other anomalies or peculiarities apt to provoke this anomaly, insensibly connects the purely hereditary pathological appetite with that which is simply the effect of acquired vicious habits. In this way a strong hereditary predisposition may exaggerate a moderate normal sexual appetite, or may give it a pathological direction under influences which would have had no effect in a less predisposed individual. Again, a slightly marked tendency to homosexuality in a man may increase under the seductive influence of a passionate invert, when the same individual would have lost this tendency if he had fallen seriously in love with a woman. On the other hand, the invert would have no influence on an individual who was not predisposed. If the hereditary disposition is very strong, it is developed spontaneously or under the influence of very slight circumstances. If it is mediocre, it may remain latent and even become extinct when favorable circumstances do not awaken it. When it is entirely absent the most powerful seduction and the most evil influence cannot give rise to the corresponding anomaly. These facts are sufficient to show what abuse is made of the term _acquired vice_. Under this heading are designated a number of peculiarities the roots of which are to a great extent contained in the germ of heredity. The power of words on the human mind produces antinomies which do not really exist; such is the case with the terms _vice_ and _disease_. Vices depend on a hereditary mnemic disposition, of varying strength and more or less pathological, or at any rate unilateral (_i.e._, developed in one direction only, or connected with a single group of objects); according to the good or evil influence of the environment they may develop, become limited or even fail to appear. Inversely, we may say that many diseases, especially of the brain, are the source of vices.