The most frequent cause for intervention during labor is insufficiency of the muscular contractions to overcome the resistance of the birth-canal. Unusual resistance of this kind explains the longer labors of women who have passed middle life before becoming pregnant. They may need to exercise more patience than younger women, though they have no greater reason to apprehend serious difficulties. Whenever rigidity of the muscles adjacent to the birth-canal arrests delivery the physician may employ the obstetrical forceps, which have been in use since the seventeenth century. Although it is widely known that physicians sometimes terminate labor in this way, the public estimate of the merits and of the limitations of the instrument is so inexact that the truth about it should be understood. Obstetrical forceps were devised by one of the Chamberlens, a family of French Huguenots who fled to England in 1569. The invention was long kept a secret; therefore its date cannot be fixed, nor even the inventor clearly identified, though everyone agrees that he was a member of this family. Clearly the instrument had been in use for some generations prior to Hugh Chamberlen, who translated from French into English the foremost obstetrical textbook of his time. The book, published in 1672, does not contain a description of the forceps, but in his preface Hugh Chamberlen refers to delay in delivery, saying, "My father, my brothers, and myself (though none else in Europe as I know) have by God's blessing and our own industry attained to and long practiced a way to deliver women without prejudice to them or their infants in this case." It is not questioned that the forceps was the secret that his ancestors and he himself employed so long and so profitably. About a century ago what are probably the original models of the instrument were discovered in a country home of Essex which once belonged to the Chamberlens; there they had been hidden in a trunk in the garret. The box in which they were concealed contained four pairs of forceps, representing different stages in their development, besides other instruments and a number of letters which established their ownership.