Thus the mind not only has within itself the propulsive force required to increase its knowledge, but also an established order, which will be steadily maintained throughout its successive and illimitable enrichment by new material; and as it grows and gains strength, it retains its "equilibrium." These continual exercises in _comparison_, _judgment_, and _choice_ carried out among the objects, further tend to place the internal acquisitions so logically into relation one with another, that the results are a singular _facility_ and _accuracy_ of reasoning power, and a remarkable _quickness_ of comprehension: the law of "the minimum of effort" is truly carried out as it is everywhere where order and activity reign. The internal coordination, like physiological adaptation, establishes itself as a result of the spontaneity of the exercises; the free development of a personality which grows and organizes itself is that which determines such an internal condition, just as in the body of the embryo the heart, in process of development, makes a place for itself in the space of the diastinum between the lungs, and the diaphragm assumes its arched form as a result of pulmonary dilation. The teacher directs these phenomena; but, in so doing, she is careful to avoid calling the child's attention to herself, since the whole future depends upon his concentration. Her art consists in understanding and in avoiding interference with natural phenomena. That which has been clearly demonstrated as regards the nutrition of the new-born infant and the first coordinated activities of the spirit will be repeated at every period of life, with the necessary modifications induced by the increased complexity of the phenomena. Continuing the parallel with physical nutrition, let us consider the growing infant which has cut its teeth, developed its gastric juice, and so gradually requires a more complicated diet, until we come to the adult man, nourishing himself by means of all the complications of modern kitchen and table; to keep himself in health, he should eat _only_ the things which correspond to the intimate needs of his organism; and if he introduces over-rich or unusual, unsuitable or poisonous substances, the result will be impoverishment, self-poisoning, a "malady." Now it was the study of the child's nutrition during the period of suckling and during the first years of life which created alimentary hygiene, not only for the child but for the adult, and pointed out the perils to which all were alike exposed during the epoch when infantile hygiene was unknown. There is a singular parallel in psychical life: the man will have an infinitely more complex life than the child; but for him, too, there should always be a correspondence between the needs of his nature and the manner in which his spirit is nourished. A _rule_ of internal life will always promote the health of the man.