The instrument should always be introduced for the first two inches with the obturator in place. The obturator should then be withdrawn and the speculum pushed farther in, the operator watching and guiding its course around the rectal valves or folds of mucous membrane, so as to prevent injury to the walls of the rectum. Anesthesia is not necessary for this procedure. =Examination of the Bladder.=--It will readily be understood that all the hollow viscera are much more easily examined when their walls are separated by distention with air than when the walls are collapsed. The bladder is most readily examined in this way. The woman should be placed in the knee-chest position, or in the dorsal position with the hips elevated above the abdomen. In either position the intestines fall from the pelvis, and when the urethra is opened air enters and distends the bladder. This distention is most certainly accomplished in the knee-chest position. In women who are not very fat, however, the extreme dorso-sacral position is equally good. The details of this method of examination are described on a later page. _The uterine sound_ is an instrument by which the length of the uterine cavity may be determined (Fig. 15). The sound, which is a large surgical probe, somewhat curved to adapt itself to the normal shape of the uterine axis, is made of pliable metal, so that the curvature may be changed readily to suit any case. The sound is graduated, and at a position of 2½ inches from the tip is a small elevation marking the length of the normal uterine cavity. [Illustration: FIG. 15.--Uterine sound.] The uterine sound was at one time used a great deal to determine the length and direction of the uterus, and perhaps to assist in determining the character of the uterine contents or of the endometrium. With our present methods of examination, however, the sound is of but little if any use. The size and direction of the uterus can in nearly all cases be determined by bimanual examination. The use of the uterine sound is by no means free from danger. Many cases of septic endometritis and salpingitis have been caused by it, and the physician has often unintentionally committed an abortion by passing the sound in a pregnant woman. The uterine sound should never be used in a routine way. It should never be used unless one expects to determine with it something that cannot be determined by simpler methods of examination. The most thorough aseptic precautions should be observed when the sound is introduced. The vulva, vagina, and cervix should be cleaned and the sound should be sterilized. The sound should never be introduced if there is any suspicion of pregnancy.