Sentence:  By keeping the <WSD>handle</WSD> of the bellows fixed in any given position the lung within the chamber could be kept for a short time at any desired degree of distension, and by pressing at intervals upon the bag, air could be forced to and fro between the bad and the lung outside the chamber, without distending the air within it. 
Meaning of the word marked with <WSD> tags:  The part of an object which is (designed to be) held in the hand when used or moved.