Very different are the phenomena of acute torsion. Here the vascular supply of the tumor is so suddenly and markedly interfered with that most urgent symptoms immediately arise. The interference with the circulation depends upon the amount of the twist and the character of the pedicle. The effect is first felt by the veins, which are more compressible than the arteries; the venous blood-current becomes obstructed, while the arteries remain open. Venous engorgement of the cyst results; extravasation of blood takes place in the walls, or the veins may rupture and hemorrhage may take place into the cyst-cavity. Death from acute anemia may result from this cause. Thrombosis and necrosis of the tumor may occur as a result of acute torsion. =Rupture of Ovarian Cysts.=--Rupture of an ovarian cyst is an accident of not infrequent occurrence. It is probable that small cysts rupture and refill without the attention of the woman or the physician being directed to the accident. The scars of old ruptures are frequently found on the surface of ovarian cysts. Wells found rupture of the cyst 24 times in a series of 300 ovariotomies. There are various causes which predispose to rupture or lead to it. As the cyst enlarges, the walls become very thin as a result of the distention. The cyst-wall may undergo, in places, retrograde changes--atrophy and fatty degeneration. The wall may become weakened as a result of suppuration, thrombosis, and the results of torsion of the pedicle; and, as has already been said, papillomatous growths destroy the integrity of the wall and lead to perforation. The immediate cause of the rupture is usually a sudden jar or a fall. Sometimes very slight pressure is enough to rupture the cyst. The manipulations of a physician, turning in bed, and coughing have caused this accident. The effects of rupture depend upon the character of the cyst-contents. Hemorrhage may be profuse and rarely fatal. The hemorrhage, however, is usually not severe, because the rupture takes place in the attenuated part of the cyst, which is but poorly supplied with blood-vessels. If the fluid is unirritating to the peritoneum and contains but little solid material, it is often readily absorbed by the peritoneum and passed off by the kidneys. Large quantities of fluid may be absorbed and eliminated in this way. A case has been reported in which the rupture of a cyst was followed by profuse diuresis which lasted four days, during which time 65 pints of urine were discharged. Another case has been reported in which the cyst ruptured and refilled 34 times during a period of nine years. The fluid on each occasion was absorbed by the peritoneum and discharged by the kidneys without in any way incapacitating the woman. If the cyst-contents are septic, as is often the case in dermoid cysts, fatal peritonitis will result. The danger of rupture of the papillomatous tumors--general papillomatous infection of the peritoneum--has already been described.