. . . . . . . . . . "???Interstitial cavity,??? as the term is used herein, encompasses interstices in a tissue or structure of a natural body structure, spaces and gaps existing between layers of tissue or existing within organs, and can include interstices within the interior of the ureter, bladder, intestines, stomach, esophagus, trachea, lung, blood vessel or other organ or body cavity, and will be further underst" .