We have learned that forty weeks are required for the full development of the human embryo, but this fact carries no assurance that pregnancy will last so long; in reality, it may end abruptly at any time. If growth is interrupted before the twenty-eighth week (the seventh lunar month), the infant will be too immature to live. Even when born alive, it will usually perish within a few hours, or a few days at most. Children born during the seventh month have occasionally survived; but the prevalent belief that they are more likely to do so than if born a month later is erroneous. That superstition originated at a time when great virtue was ascribed to numbers. Since seven was a sacred number, it was considered more auspicious to be born in the seventh month than in the eighth. Universal experience, however, teaches us that the likelihood of rearing a premature child is, by a rapidly increasing proportion, the greater for every week that it remains within the uterus. This is precisely what we should expect, for the period of its existence there measures the perfection of its development; and that, under ordinary conditions, determines how strong and hardy the child will be. Although during the first six months the outlook for the infant will be equally unfavorable at whatever time pregnancy may be interrupted, physicians prefer to distinguish cases which terminate in the earlier part of this period from those which terminate in the latter part. For technical reasons, the sixteenth week represents a natural point of division. A birth which takes place before that time is called an abortion; one which takes place between the sixteenth and the twenty- eighth week is called a miscarriage. The anatomical reasons which justify such a distinction do not concern us here, and the matter deserves mention merely because the same terms are often employed in a very different sense by the laity. As most of us know, the interruption of pregnancy results sometimes from purely natural causes, and sometimes from the employment of artificial means. As a rule, persons who are unacquainted with medical terminology call a birth of the former kind a miscarriage, and reserve the term abortion for an interruption of pregnancy that is deliberately provoked. Physicians, however, make no such distinction. They use these words, as I have said, simply to indicate how far development has progressed before the termination of pregnancy. Since the term abortion is apt to carry with it the implication of a criminal act, confusion will be avoided if we agree for the time to depart from strictly medical usage and designate as miscarriage the spontaneous termination of pregnancy prior to the twenty-eighth week.