These comprise all the signs and indications of pregnancy that possess any real value. Some of them, at certain times, and under particular circumstances, may be called _positive_; such as those discovered by Ballotment and Auscultation, and also the presence of Kyestein in the urine. Most of the others merely make it _probable_ that pregnancy exists, or warrant us in presuming as much. They are not to be depended on implicitly alone, but when many of them are observed together, and no other cause can be assigned for their production, the presumption becomes so well supported as almost to be called a moral certainty. A person of experience, who is familiar with all these signs, and with the others produced by disease which resemble them, will seldom find it difficult to decide; but still there are cases in which pregnancy proceeds, even to its termination, with but few unusual symptoms, so that both patient and attendant are completely at fault. This however is very rare, and many eminent authors contend that it is _always_ possible to detect pregnancy, _after the sixth month_, and I think so myself, unless the child be dead, in which case it will soon be evident in another way. CHAPTER VI. DURATION OF PREGNANCY. The duration of pregnancy, or the precise term of Utero Gestation, is not fixed. It appears, from accurate observation, that there is no absolute period determined by natural laws, and therefore there is none laid down by human enactments. An approximation can be made, by taking the average of a number of cases, and the period of limitation may also be determined in the same way. The most usual period is about nine months, or from thirty-five to forty weeks, some females going beyond the thirty-six weeks, and others not so long. First children are frequently born under the nine months, and more so than those that come after; this is a fact not generally known, and ignorance of it has often given rise to unjust suspicions. It is quite possible for a female to be delivered, with the child at full period, in a little over eight months after marriage, without there being any just grounds whatever for suspecting unfaithfulness. Dr. R. Lee, in his Lectures on the Theory and Practice of Midwifery, gives the best summary that we have in the language, of our information on this subject; I will therefore quote from his work, making such comments and additions as I may think advisable.