However frequently and warmly the theory of the origin of chorea in a neuropathic predisposition was advocated by Charcot, the fact of its usual evolution consecutive to some toxic or infective process is no less certain. Its incidence is greatest in children and the adolescent; it runs a regular course of increase and decrease; and the circumstances which cause the symptoms to vary during this cycle are never sufficiently potent to bring about even transitory suppression of them. It is true that changes in the intensity of the symptoms seem to confer a remittent character on the affection, but there is nothing at all comparable to the sudden and unexpected waxing and waning of the form of chorea at present under consideration. None of the pathological attributes just mentioned concerns variable chorea, which, in addition, differs from Sydenham's chorea in two points--the multiplicity of the types of movement, and the fact that the patient can voluntarily check his involuntary actions. For these reasons, assimilation of the two clinical varieties is impossible, and the confusion of the two in practice need never occur. A form of chorea entitled "habit spasm" by Gowers, and "habit chorea" by Weir Mitchell, has been the subject of further study by Sinkler,[179] but in all probability the cases of this description reported are instances of the variable chorea of Brissaud. B. Huntington's Chorea In spite of the preponderating etiological significance of heredity and the constancy of psychical imperfections in the chronic chorea of Huntington, its confusion with tic is not at all likely to occur. Difficulties might arise in distinguishing chorea major from variable chorea, however, and here we have the views of Brissaud to help us. True chronic chorea is an incurable neurosis, of life-long duration. We have no trouble in pronouncing a diagnosis of chronic chorea if the symptoms date back five, ten, or twenty years, but they must have had a commencement, and the whole problem is to foretell the course of a chorea as yet only a few weeks or months old. The involuntary movements of chronic chorea, like those of Sydenham's chorea, are illogical, but they are combined in a co-ordinate manner--that is to say, certain functionally associated muscular groups act simultaneously as for a particular end: the patient shrugs his shoulders, closes his fists, cracks his fingers, utters cries, he swallows, sniffs, sucks in his breath, makes the sound of kissing, etc, in all of which actions orderly participation of the musculature in a foreordained way is evident. Slight twitching of individual muscles and parts of muscles also occurs.