Abstract: A nursing bottle assembly of the type in which a collapsible liquid sack having an open end and a closed end and is contained in a protective tube open at both ends that is provided with a plunger for expelling air from a collapsing liquid containing sack. The open top end of the sack is clamped by a nipple mounting cap to one end of the tube. The hollow cylindrical plunger can be inserted into the open end of the protective outer tube opposite its nipple carrying end. Any time liquid is being or has been withdrawn from the sack, the plunger may be manipulated by manual pressure to compress the sack toward the nipple end of the tube to reduce the volumetric capacity of the sack between its closed end and the nipple to prevent any air from accumulating in the sack space vacated by the removed liquid.