Observe that nature always responds to rhythm. The body will respond to rhythm. Let the exercise be taken vigorously and definitely. Let also the reactions or rests be equally definite and decided. Vigor should never lead to constrictions or to great labor. If we lie on our back and stretch one side and then the other it is easier and we accomplish better results as a rule than we do by stretching both arms and feet simultaneously. It is hard to explain the sympathetic union of co-ordination and rhythm. I have never found any explanation or even reference to this. Even Dalcroze, who has so many good ideas regarding rhythm, has not grasped the principles of co-ordination of different parts of the body and especially the relation of co-ordination to rhythm. Awkward people lack both co-ordination and rhythm and the two are vitally connected. By establishing co-ordinations we begin to establish rhythm, and by establishing rhythm we help in the co-ordinations. The principle of rhythm applies to all our human actions. We should walk rhythmically, and we should stand allowing all the rhythmic curves of the body to have their normal relationship. We shall always have the right rhythmic curves if we have the right centrality and co-ordinations. One of the greatest effects of music is due to the rhythm. All movements, however, have a rhythm of their own. 11. Use in every exercise, as far as possible, all the primary actions of the muscles. We can distinguish four actions of the muscles. First, active contraction, shortening of the muscles sometimes called concentric contraction; secondly, we can stay the tension of the muscles at a certain point. This is called static contraction. Third, we can allow the muscle gradually to release its contraction, that is, allow it to slowly lengthen. This is called eccentric contraction. Fourth, we can take the will entirely out of a muscle and allow its complete quiescence. Rhythm demands the presence of all these actions; and also all these elements in proportion. And in the practice of all exercises it is well to accentuate all four of these elements by counting. In the stretch for the whole body, for example, we can extend the limbs slowly as far as possible, and there will be a contraction of the extensor muscles. Then we can stay the body when stretched to the fullest extent. Then we can gradually release the action of these muscles and then completely rest. Some of the exercises can be practiced with dual movements, first with activity and then release, but by varying the climactic action for a moment and gradually releasing, that is, by giving these a quadruple rhythm, we can accomplish better results than in the dual.