To imitate, in Littré's definition, is "to seek to reproduce what another is doing." How such an act is to be accomplished without the co-operation of the will we cannot conceive. Its duration being so brief, our recollection of the conscious stage may be very imperfect, but that is no ground for denying its reality. Involuntary execution of a gesture to-day does not exclude the possibility of its voluntary execution yesterday. If we find accurate reconstitution of the steps in our own habitual mental processes impracticable, _a fortiori_ ought we to question the likelihood of our gaining full insight into the mechanism of the processes of others. It is no doubt this perplexity which has induced Cruchet to regard the simple convulsive tic as the sole manifestation of the disease. On his own admission, nevertheless, this simple convulsive tic is of exceptional occurrence, apart from children, in whom mental trouble is conspicuous by its absence. But the psychical disorders of infancy, however embryonic they be, are none the less real. Their insignificance may hinder their recognition, yet they are often the prelude to graver and more definite anomalies in later life. And if their detection demands painstaking study and repeated interrogation, fruitless results may very well mean that the investigation was not sufficiently thorough. Moreover, the view that regards imitation as a prolific element in the genesis of tics has met with widespread acceptance. The onset of the disease (says Guinon) is sometimes the consequence of the patient's partiality for mimicry. Contact with an affected person supplies the occasion. His first experience is a sort of constant preoccupation; the other's grimace is ever before his eyes, inviting imitation; at length he suddenly yields to the obsession, and his tic is in the making. Reference has already been made to a case of Tissié's,[36] where an eight-year-old child acquired from its mother an ocular tic, which a second child imitated in its turn. The cure of the latter was followed with the cure of the two others, _by imitation_. The word "echokinesia" was imagined by Charcot to specify the inclination some people show to copy what they see others doing. It has also received the names of "mimicism" and "imitation neurosis." To quote Guinon again: The movements most closely and most infallibly mimicked are facial. These the patient either is driven actually to reproduce, or feels impelled to reproduce, without allowing the impulse to pass into action. Simple and circumscribed gestures involving the limbs are similarly, if less frequently, the object of imitation. Such tricks as rubbing the nose or cheek or some other part, or stooping as if to pick up something on the ground, may be counterfeited in their entirety, though at other times the movement is only initiated.