1. The essential, principal, fundamental cause which, after the period of physiological incubation, gives a determinate direction to the tendency is constitution, temperament, character. It may be admitted, at least theoretically, that _all_ tendencies exist, actually or potentially, in every one of us. In ordinary cases, one or more predominate. Contemporary research has familiarised us with the fact of the varieties of memory. Such and such a person has an excellent one for figures, or music, or colour, or form, but only moderate for everything else. This is a natural gift singularly capable of being developed by exercise. This fact has its equivalent in the motor order, or that of tendencies: there exist natural dispositions only wanting an opportunity to become preponderant, and morbid conditions are the culture-medium which favours their development. The most violent tendency has its source in normal life. “There is,” says Gall, “an inclination gradually rising from the pleasure of seeing anything killed to the most overpowering desire to kill.” This is not put strongly enough; it is possible to pass, by imperceptible gradations, from the extreme case to the normal state in the following order: the pleasure of killing, the overpowering desire to kill, the pleasure of looking on at killing (the sight of a murder, gladiatorial combats, etc.), the pleasure of seeing the blood of animals shed (bull-fights, cock-fights, etc.), the pleasure due to the representation of violent and bloodthirsty melodramas (this is only in appearance, but the stage always presents a momentary illusion of reality); lastly, the pleasure of reading bloodthirsty novels, or hearing accounts of murders, which is purely an affair of the imagination. We thus pass from the act to the perception, the simulacrum, the mere image suggested by signs read or heard. I do not wish to assert, assuredly, that the spectators of the drama or readers of the novel are all potential murderers; but, as there are other men to whom such sights and such reading are abhorrent, we must recognise certain differences of natural disposition. Now the peculiarity of retrogression (or degeneration) is to act on the line of the strongest attraction or the least resistance, which is a characteristic of reflex action and the opposite of the inhibitive will, which acts on the lines of weakest attraction and strongest resistance.