If we were to confine ourselves to this description by Sydenham, which so far as typical cases of the disease are concerned is perfectly accurate, differentiation between tic and chorea would not be a matter of any complexity. Unfortunately, however, the varieties of this form of chorea are legion, and in practice one constantly meets with conditions suggesting alike the gesticulations of chorea and the convulsive reactions of tic. Moreover, it has been pointed out by Oddo[177] that the fact of the habitual exaggeration of tic during the very years when chorea is liable to appear is calculated to confuse the issue. He has attempted, however, to specify certain factors in the differential diagnosis. In the first instance, the form of the movements is of significance: there is no co-ordination in the muscular play of the choreic; it is amorphous, indefinable, and erratic, whereas the gestures of tic are purposive, and may be said to have a shape. One never sees in chorea a succession of similar movements, but though a patient be suffering from several tics, each of them is reproduced always in the same fashion. Unilaterality of distribution is more common in chorea than in tic; in other words, chorea, more or less, follows anatomical lines in the regions it affects, whereas the incidence of tic is physiological. Both are arhythmic in their manifestation; nevertheless the repetition of tic is noteworthy for its regularity as compared with the changing mode and rate of the other. Noir emphasises the diagnostic value of its frequency, abruptness, and reiteration of identical movements. In a majority of cases the interference of the will is futile as far as chorea is concerned, while the victim to tic is usually capable of restraining his muscular activity at least for a space. The choreic exhibits his movements in public, but the _tiqueur_ seeks the seclusion of his own room. The association of tic with obsessional ideas is frequently encountered, but there is no similar connection between obsessions and chorea. In addition, the myasthenia, pains, and alterations in the reflexes that often characterise chorea are awanting in the other affection. It cannot be gainsaid, however, that the frequency with which atypical varieties of chorea occur is inimical to a ready diagnosis, and the onerous nature of the task is not lessened by the circumstance that many choreics are the offspring of neuropathic parents and reveal psychical anomalies comparable to those of the subjects of tic. In a disease such as variable chorea, which has features in common both with tic and with chorea properly so called, the problem of diagnosis is still more complicated, though excellent hints for its solution have been furnished by Brissaud.[178]