_Period for performing the operation._ Although under the head of PREMATURE EXPULSION we have stated that a foetus is capable of maintaining its existence if born after the twenty-eighth week of pregnancy, we must not be supposed to recommend the artificial induction of premature labour at so early a period as this. "Experience has shown that it was not necessary to induce labour at so early a period as was first imagined, on account of the very great difference which even one or two weeks are found to make in the hardness of the foetal skull. Thus, for instance, in cases where the antero-posterior diameter was only three inches, six weeks before the full term of utero-gestation were found sufficient, and where it was three inches and a half, fourteen days made sufficient difference." (Naegelé, _MS. Lectures_.) Still, however, as it is so difficult to be quite sure of the data upon which we have made our reckoning, it will be safer to fix the operation a week or two earlier; and if we lose a little time by failing in our first endeavours to induce uterine action, it will be of so much the less consequence: hence, therefore, as a general rule, the most eligible time will be between the thirty-fourth and thirty-sixth week; and if the deformity be very considerable, we may commence operations as early as the thirty-second week or two months before the full term, short of which it will seldom either be justifiable or necessary. On the other hand, where the state of the cervix and the history of her pregnancy combine to make our reckoning nearly a matter of certainty, the later we can safely delay the operation the better, for by so doing the process resembles more a natural labour, and the chances in favour of the child are much increased.