I may say that in the physical aspect of tics we have a specific somatic manifestation which, if explained, should, in a way, be the gateway toward the understanding of the many somatic symptoms which we find in the psychoneuroses and psychoses.
THE EVOLUTIONARY, PHYLOGENETIC STANDPOINT
A year or more before Clark's paper appeared, I had arrived at certain general conclusions regarding the subject of tics.
G. Stanley Hall has arrived at similar conclusions in his inspiring Synthetic Genetic Study of Fear[8] and I wish here to acknowledge my indebtedness to his paper for making my own ideas clearer to me, for having given me broader standpoints and for clearly presenting a theory which shall form the basis of the remainder of this paper.
[8] In the American Journal of Psychology, Vol. XXV, in the July issue et seq.
Let us first take up the tic movements and see whether we can arrive at a rational explanation for their appearance.
The different varieties of tic movements embrace the entire field or range of systematic, physiologically coordinated voluntary muscular activities.
The main types of tics may be enumerated at this point: facial tics, which are the most frequent and which may be tonic or clonic, are tics of mimicry and express emotions; tics of the ear or auditory tics; nictitation and vision tics, particularly of the eyelids; tics of sniffing; tics of sucking; tics of licking; tics of biting and of mastication, and mental trismus; tics of nodding, tossing, affirmation, negation, salutation and mental torticollis; trunk, arm and shoulder tics; snatching tics; the professional or occupational spasms, which are really a special atypical form of tics; walking and leaping tics; tics of spitting, swallowing, vomiting, eructation and wind sucking (aerophagia); tics of snoring, sniffing, blowing, whistling, coughing, sobbing, hiccoughing; tics of speech, including all sorts of sounds, stammering (in some cases), habit expressions, echolalia and echopraxia.
It is thus seen that we have here physiological and biological acts of different manifestations and purposes.
The tic movements have a certain significance at the time of their performance. The physiological functions are definite.