[Tics are not the private property of the human species. The word appears to have been first employed in reference to horses, and while little attention has hitherto been paid to the subject in veterinary annals, its methodical study has recently been undertaken by Rudler and Chomel.[29] It is remarkable how intimate are the analogies established by these observers not merely between the tics of animals and of mankind, but also between their respective mental conditions. Physical and psychical stigmata of degeneration are as obvious in the horse that tics as in the man who tics, and it is not without interest to note that the tics of such animals as have the most rudimentary psychical development present a close resemblance to those that occur among the least advanced of the human race, among idiots and imbeciles.] CHAPTER V THE ETIOLOGY OF TICS The circumstances favouring development of a tic in soil already prepared by psychical predisposition are manifold. Our studies in the pathogenesis of tic have illustrated the significance of exciting causes, so-called. We have seen how the motor part of the tic was originally directed to some definite object, and therefore provoked by some definite cause, and how the eventual disappearance of this cause does not justify the conclusion that it has never existed. We shall be able to quote numerous instances in point when dealing with the different localisations assumed by the tics; what we wish to remark here is that the initial cause is by no means always easy to ascertain. The subjects of whom we are treating exhibit a vexatious tendency to invent a more or less fantastic etiology for themselves, and their statements cannot be accepted without rigorous investigation. Of any actual exciting cause they may be really ignorant, or more likely oblivious. In this connection an important case is reported by Pierre Janet[30]: A young man twenty-five years old was affected with a facial tic in the shape of constant grimaces, accompanied by violent expirations through one nostril. Six years of the condition had neither enabled him to determine its origin nor brought him any relief. He presented, in addition, the phenomena of automatic writing and was the subject of somnambulism, and when in the latter state explained that the tic arose from the effort to expel an irritating nasal obstruction due to an epistaxis six years ago. Needless to say (adds Janet), there never had been any obstruction in the nose; the truth was that in the somnambulistic state he was reminded of a subconscious fixed idea of which he was ordinarily unaware. Recognition of the causal factor, then, is not without value, as otherwise the tic's situation and form may rest inexplicable. These exciting causes we shall discuss more closely at a subsequent stage, confining our attention for the present to one or two general considerations.