Man often means one thing while God means another. Luther meant to reform the Roman Church--God meant to reform the world. Dr. Clarke meant, as he tells us in his preface, to excite discussion, and stimulate investigation, with regard to the relation of sex to education; but he has excited a discussion, and stimulated an investigation, that, unless Ephraim is wholly joined to his idols, will not stop until a reform has been wrought in our whole social system. Not only in our colleges and universities, but in our lower grades of schools; and--as he has taught us that the head is not all, but the body a good deal--in our food, in our times of downsitting and uprising, in our hours of retiring, in the ventilation of our churches, public halls and private homes. We are at last to understand, what it is so hard for an American to understand, that to wait is sometimes as much a duty as to work. Dr. Clarke meant to prove, that co-education, in the popular signification of that term, for physiological reasons, is an impossibility. He succeeded, as he thinks, theoretically, but failed, as he confesses, practically, for the want of sufficient data. What he indirectly proved was of much more vital importance, because it affects the whole nation; that, for physiological reasons, American women, and consequently the American people, cannot live at this high-pressure rate, which means death. The universal interest which his book has awakened, the rapidly following reviews and criticisms, the numerous essays which have since been published, on the same and kindred subjects, show that thinking minds were already working their way to definite conclusions and expression on this now most important of all subjects--how to give back to the American woman the bloom and physical strength, the elasticity and fresh old age which are hers by the right of inheritance. No one will deny Dr. Clarke's statement, that, with the best of opportunities, she does not in these respects compare favorably with her trans-Atlantic sisters. But we are not willing to admit that the strength of the German _fraeulein_ and English damsel must be purchased at so great a sacrifice as the giving up of all systematic study, and consequently of all higher intellectual development.