To open the mouth and neck of the pregnant uterus artificially is difficult under favorable conditions; to do so when the conditions are unfavorable is one of the most trying operations in all surgery.
Under some conditions of the os and cervix, manual dilatation is more or less easily accomplished, but there are other cases in which the fingers are utterly useless. Consider the tissues to be overcome—a fibromuscular canal so firmly closed normally that with all the burdensome pressure of gravidity it remains intact, even the force of strong labor causing it to yield only after many hours of exhausting effort. If it takes Nature ten or fifteen hours to effect an opening, what shall be said of a device that will accomplish such a feat within an hour and do it safely?
While the hand is a dilator always at command there are disadvantages accompanying its use. First,