With increasing cortical development the individual is able, on stimulation no longer peripheral but central in origin, spontaneously to execute movements which frequent repetition has endowed with all the features of functional acts. Of these ideomotor phenomena physical exercises, games, manual trades, readily furnish instances. Swimming, for an instance, requires the rhythmical co-ordination of arm and leg, to attain which perseverance, retentiveness, and above all repetition are essential. At length the time arrives when the swimmer is surprised at the absence of any necessity for voluntary co-ordinating effort on his part. In fact, to reintroduce volition into this acquired automatism would be to court disaster. "What I do naturally," said Montaigne, "I can no longer perform if I attempt it expressly." From these physiological considerations we are led to make the following classification of motor reactions: 1. Simple spinal reflexes, innocent of co-ordination or functional systematisation, on whose production or inhibition the will has no influence. To this division belong the movements known as spasms. 2. Functional motor acts. Among these we may distinguish: _a._ Essential movements, _e.g._ respiration, suction, etc., appearing at birth, and co-ordinated in view of some definite function. _b._ Acts such as locomotion, mastication, etc., whose acquisition is subsequent to a more or less prolonged period of education. _c._ Non-essential ideomotor acts, acquired later in life, which soon assume all the characters of functional acts. The movements belonging to the first group in this latter category may manifest themselves without any exertion on the part of the will, but its activity is essential to the perfecting of the second, and the originating of the third. In this last division are placed the motor phenomena known as tics. TIC AND CO-ORDINATION We have thus come to see that a tic is a co-ordinated, systematised, purposive act. The majority of observers are satisfied on this point, although there exist various differences of opinion, more apparent than real, the inevitable result of disagreement as to the interpretation of certain expressions. It is imperative to obviate misunderstanding once and for all. In his first contribution to the study of the disease which bears his name, Gilles de la Tourette gave the general description of _motor inco-ordination_ to the convulsive movements of his patients. It has been argued by Guinon, on the contrary, that they are really systematised, and that they reproduce, in an involuntary manner, the co-ordinated movements of everyday life. That this is sometimes the case Tourette subsequently admitted, but he still professed their frequent actual inco-ordination.