With a child's delight the worthy battalion commander gravely made ready to speak. He readjusted his polished shako on his head, and gave that twitch of the shoulder appreciated only by such as have served in the infantry--that twitch which is meant to raise the knapsack and momentarily to lighten its load; it is a trick of the soldier's which with his elevation to officer's rank becomes a tic. Another sip of wine followed this convulsive gesture, a kick of encouragement in the little donkey's stomach, and he began.... The description could not have been more accurate. The passage from the voluntary to the involuntary--the kick too may have been a tic--and the obvious infantile traits in the old gentleman's character, make the picture remarkably complete. Apart, however, from the causes we have just enumerated, and others to be noticed below, we must emphasise the fact once again that mental predisposition is a _sine qua non_ for the development of tic. CHAPTER VI PATHOLOGICAL ANATOMY Our ignorance of the pathological anatomy of tic is profound. Hitherto all the cases labelled tic in which a post-mortem examination has been made have in reality been spasmodic affections differing essentially from the tics as we understand them, according to the ideas of Trousseau, Charcot, and Brissaud. As far as we are aware, not a single sectio of a genuine case of tic is on record where a lesion, of whatever nature or whatever site it be, has been discovered to which the tic might be attributed. Either an autopsy is not obtained, or if it is, no special abnormality is remarked, or else the diagnosis has been erroneous and the changes described have not been those of tic. It would be premature, of course, to conclude that tic is a disease _sine materia_. The affirmation is quite unwarranted. As is the case with numbers of neuroses and psychoses, we must for the present rest satisfied to observe symptoms; the mystery of their morbid anatomy will remain unsolved until our methods of investigation attain perfection. Magnan[39] says of "superior degenerates" that clinical observation reveals functional disorders so distinct and so invariable that it is impossible they should not be the outcome of some pathological modification of the organism. It is true he declares in another place[40] that the mentally unstable have all a family likeness, consisting not in identity of well-defined anatomical lesions, but in similarity of functional derangements. As it is, from the motor point of view tic is a functional act, and the governing centre is a functional centre that has become hypertrophied, so to speak, by being educated to excess. This physiological centre must not be confused with the "centre" of current anatomical terminology; it does not exercise an exclusive control over a particular territory--several such may co-exist in a single anatomical area.