This case is also remarkable for two other facts: one, "that a woman in perfect health, and pregnant with a healthy child, may exceed the period of nine months by several days; the other, that a check is not always immediately given to the catamenial flow by an ovum being impregnated." Probably it is not so generally so as many suppose. The term of utero-gestation, or the length of time from conception to the commencement of labor, is not precisely determined by physiologists. "It seems, however," says Dr. Dewees, "from the best calculations that can be made, that nine calendar months, or forty weeks, approaches the truth so nearly that we can scarcely need or desire more accuracy, could it be obtained." Unquestionably, however, some cases exceed this period by many days, or even weeks, and it has been a question much agitated, how far this period is ever exceeded. It is a question of some moment in a legal point of view. Cases are reported where the usual period was exceeded by five or six months; cases, too, where the circumstances attending them and the respectability of their reporters are such as to command our belief. Dr. Dewees has paid much attention to this subject, and he declares himself entirely convinced "that the commonly fixed period may be extended from thirteen days to six weeks, under the influence of certain causes or peculiarities of constitution."* * See tables in Dr. Bull's "Hints to Mothers," pp. 130-141. --Publishers' note. These occasional departures from the general rule will, perhaps, be the more readily admitted when we consider that they are not confined to the human species. From the experiments of Tessier, it appears that the term of utero-gestation varies greatly with the cow, sheep, horse, swine and other animals to which his attention was directed.