The frequency of the muscular contractions in tic is so very variable that it cannot be regarded as a distinctive feature, nor is there any evidence to show that it is rhythmical, as some would have us believe. Contrary to what obtains in tremor, there is no periodicity in the motor phenomena, even when the tic is based on derangement of a function whose manifestations are rhythmical, such as the function of respiration. Conditions described as rhythmic tics, or less well as rhythmic spasms, seem to form a group by themselves; probably they do not belong to the same family as the tics, indeed in some cases they are symptomatic of encephalic lesions, as in the _spasmus nutans_ of infants, or the rhythmic tics of idiots and imbeciles. In this connection the remarks of Noir are very pertinent: We shall be well advised to refrain from drawing too absolute conclusions in questions so difficult, where even the framing of an hypothesis demands prolonged observation, but we cannot withstand the temptation to note the co-existence of certain of these tics with certain definite lesions recognisable post-mortem. This has been done before us by our master Bourneville, who has on several occasions made the diagnosis of chronic meningo-encephalitis, cerebral sclerosis, etc., from this association of rocking, rotation, and krouomanic movements with a special symptom-complex, and verified it at the autopsy. Nevertheless, there is not always an absolute correspondence between them, wherefore Bourneville, with an altogether praiseworthy scientific reserve, has hesitated to consider these tics as actual symptoms of the affections alluded to, and we shall follow his prudent example. To the combination of various rhythmical acts with hysteria we shall revert at a later stage. Under the title "rhythmic spasm" an interesting case has been reported at length by de Buck,[55] concerning a young woman, free of hysterical stigmata, in whom convulsive movements first appeared at the age of seven years.