The operation may have been conducted aseptically and the tissues be healthy, but the ligature becomes infected by the admission of air as a result of drainage, or implication of the bowel or bladder. I made a careful study of the fate of silk sutures employed in pelvic surgery extending over many years, and came to the conclusion that, even under favourable conditions, silk ligatures disappear very slowly. The silk used to secure an ovarian pedicle may, in very favourable circumstances, disappear in twelve months, but the knots require nearly double that time. The piece of silk which encircles the Fallopian tube is apt to behave in a curious way; in 1898 I removed an ovarian cyst the size of a fist, and tied its slender pedicle with thin silk. Although the recovery was uneventful, the patient complained during many weeks of cramp-like pains on the side from which the cyst was removed. These pains gradually subsided, and ten months later, during menstruation, the patient noticed on the napkin a tiny loop of silk, which she saved. This was the loop of silk which secured the Fallopian tube; it had ulcerated into the tube and been conducted into the uterus and escaped. I have since had a like condition, the loop making its appearance three weeks after an ovariotomy. It has been established by experiments on the long uterine cornu of rabbits, that an encircling ligature will ulcerate through, leaving the lumen of the cornu intact. Clinical observations regarding ligatures applied to Fallopian tubes in the performance of Cæsarean section for the purpose of preventing pregnancy prove that this is a useless measure (see p. 71), for these tubes in many instances have recovered their patency, and pregnancy has recurred. It is a fair inference that the ligature ulcerates into the lumen of the tube, which then heals behind it, without stricture of the canal. A similar condition of things sometimes arises after Cæsarean section, especially when the uterine incision is closed by two layers of sutures. Those sutures which involve the endometrium will ulcerate into the uterine cavity and cause irregular slight losses of blood until they escape. It is important to emphasize the fact that silk sutures in uterine tissue will, in some instances, remain unabsorbed for many years. A patient who had been submitted to Cæsarean section in 1903 came under my care four years afterwards for the removal of the tumour which caused obstruction; the sutures used to close the uterine incision were visible, and a microscopic examination showed that each silk suture was enclosed in a fibrous tissue sheath (Fig. 28).