These exciting causes we shall discuss more closely at a subsequent stage, confining our attention for the present to one or two general considerations.
Age.—Tics may occur at any period, except in infancy. "Nervous movements" appearing previous to the age of three or four cannot be tics, as has been made plain in the chapter on pathogeny. It is only with the development of psychical function—about the age of seven or eight—that revelation of its imperfection, if such exist, becomes possible.
Initiation or exacerbation of a tic is very frequent about the time of puberty, when both physical and mental evolution is peculiarly apt to suffer interruption.
Sex.—Sex is without influence on the disease.
Race.—In spite of the absence of precise statistics on the subject, the opinion that the tendency to tic increases with the advance of civilisation is not, we think, premature.
We have had the curiosity to interrogate several travellers familiar with different savage tribes of Central Africa, who, although notified beforehand to be on the look-out, declare they have practically never met with tic in negroes. These observations require to be confirmed.
It may be questioned if the level of mental attainment of such primitive peoples is sufficiently high to allow of the establishment of tics. Their occurrence in the lower animals has been recorded, it is true; but with our ignorance of what constitutes an animal tic, and until further information is forthcoming, it is prudent not to speculate on these matters. We must be content with the remark that savages and animals are less exposed than the civilised to circumstances facilitating the development of mental instability.
Trauma and infectious disease may provide the occasion for either the appearance or the disappearance of a tic, but of themselves they are incapable of originating the affection.
One of Noir's patients had a brother similarly afflicted, and a sister in whom an attack of bronchitis at the age of five was accompanied by tics of arm and head, which recurred subsequently in an exaggerated form during smallpox. On each of two occasions on which J. suffered from influenza his tics increased in violence and extent; while in the case of G. aggravation heralded the approach of measles.
Young M., on the other hand, remained free of all his face and head movements during the immobilisation of a fractured leg, with the cure of which his tics returned.