When Metchnikoff believed he had discovered that the leucocytes in the blood absorb and digest microbes and thus save man from infection, it seemed as if a ray of clear and simple light had illuminated all the mystery. But no sooner was his theory promulgated than it was demolished by the successive studies in which it was subjected to a destructive criticism, because the leucocytes are not always able to absorb living microbes; certain "conditions" of the organism are requisite in order that they may have this power, and so the knotty point was merely shifted. Moreover, it is not the actual microbes which cause disease, but their toxines. Thus the theories of toxines seemed to be the true guide for researches; but then we entered into a sea of complications, and it is obvious that only "aspects" and "attributes" of immunity are accessible to us, but that the substance, the last word, underlying all those aspects which research has revealed is: mystery. For this reason, there is silence to-day as to questions of immunity; that which was once familiar as a popular idea remains among the obscure studies which not even the students of the university should approach. Nevertheless, it is "impossible" that the medical science founded upon natural forces should develop, unless the imperative necessity be recognized of studying the mystery of life which conceals its source, but continually expands its forces. The invisible but real source of health and healing is always there, at the climax of all efforts; and the palpitating energy which springs inexhaustibly therefrom is the only reality which makes evident this revival of the living. This medical science and this mystery cannot but form a unity. It is probable that this will be brought about by that science which studies the health and the maladies of the soul. If this should discover that the soul, too, is corruptible, subject to disease and death, that it has its laws of health and its _vis medicatrix naturae_, treatments tending to respect and aid this precious force of life should multiply immeasurably; and at the same time the mysterious source whence it gushes should impose itself on modern medicine, as the question of immunity has done. Then life, morality and religion will be indissolubly united. * * * * * Let us now turn to children of two and a half and three years old, who touch everything, but especially those objects which they evidently prefer, the most simple objects, as, for example, a square block of paper, a square inkstand, or a round, shiny bell. All things which "are not meant for them."