But how often normal persons harbor in their minds the germs of such a mania! Here, for instance, is a person who is going out; he locks the door and shakes it; but when he has gone a few steps he is assailed by doubt: did he fasten the door? He knows that he did, he perfectly remembers having shaken it, but an irresistible impulse makes him go back to see if the door is really fastened. There are children who, before getting into bed at night, always look under it to see if there are any animals there--cats, for instance; they see there are none, and quite understand there are none. Nevertheless, after a while they get out again "to see if there is anything." These germs are carried about enclosed like tubercular bacilli in some tiny lymphatic gland; the whole organism is weak. But the mischief is hidden and causes no uneasiness, just as the pallor of the face may be concealed for a time by rouge. If we consider that the will must manifest itself in actions which the body must carry out effectively, we shall understand that a formative exercise is necessary to develop it by means of its mechanisms. There is a perfect parallel between the formation of the will and the coordination of movement of its physiological structure, the striated muscles. It is evident that exercise is necessary to establish precision in our movements. We know that we cannot learn to dance without preliminary exercises, that we cannot play the piano without practising the movements of the hand; but prior to this, the fundamental coordination of movements, that is to say, ambulation and prehension, must have already been established from infancy. It is not yet so evident to us that similar gradual preparations are necessary to develop the will. In the purely physiological functions of the muscular apparatus, our voluntary muscles do not all act in the same manner, but rather in two opposite senses; some, for instance, serve to thrust the arm out from the body, others to draw it near; some serve to bend, others to straighten the knee; they are, that is to say, "antagonistic" in their action. Every movement of the body is the result of a combination between antagonistic muscles, in which now one, now the other prevails in a kind of collaboration by which the greatest diversity of movements is made possible to us: movements energetic, graceful, elegant. It is thus we are enabled to establish not only a noble attitude of the body, but a delightful motor correspondence with musical rhythm.