One of the most frequent complications which occurs to annoy the obstetrician, protract labor and exhaust the patience and endurance of the parturient, is a rigid and unyielding os. This term is applied in a general way to a variety of conditions, materially differing from each other; but possessing this feature in common—the cervical tissues are unyielding, and the os undilatable. This may depend upon non-development in the early primipara; upon fibrous degeneration in the old; upon cicatricial induration, consequent to previous lacerations, and upon pathological change, incident to carcinomatous disease. But we frequently find a persistent rigidity where none of these conditions are present; wherein the lower uterine segment is apparently fully developed, and normal in character, thin and soft when quiescent, but upon the advent of each uterine contraction the encircling tissues spasmodically contract and become rigid and unyielding. More or less sensitiveness and irritability of the cervical