must be wired or else back-leak occurs. The bulb is compressed to fill the bag, then the air allowed to leak out till the bag is about 1 cm. thick, and the manometer face is rotated till the needle stands at o.
The amount of tension in the bag or the size of the bag are indifferent matters, not affecting the record. The bag is placed under the corset at various places and the readings taken, first
at the end of quiet expiration, then at the end of full inspiration (Fig. 31).
For observations in the vagina the thin smallest size elastic rubber ice bag is made to ride upon and above a two-inch spiral spring, soft rubber, circle pessary to which it is cemented in such a way that its lower end makes a resisting diaphragm across the opening of the ring. With patients having widely torn and gaping pelvic floors, as in old prolapses, this bag is cemented above an air-filled cushion pessary. The bag is gently distended when in place and the dial rotated to bring the needle to zero,
