Upon the filing of such description and boundaries with the county board, the county board shall call an election within the entire area and submit to the qualified voters therein the question of the enlargement of such district to include all the territory within the proposed new boundaries. If at such election a majority of the combined and total vote cast by the qualified voters residing within the original territory of such sanitary drainage district, and the territory proposed to be added thereto, shall be in favor of such enlargement, such district as so enlarged shall be deemed an organized sanitary drainage district and the trustees of such original district shall be the trustees of such enlarged district until their successors are duly elected and qualified.