operation, method, performed, extent, prevent, ordinary, proper, considerable, passed, generally, improvement, drainage, improved, successful, consists, sheet, produce, apparatus, operate, removing, sufficiently, extensive, contents, loss, introduction, knife, control, advisable, continuous, producing, combined, rule, flap, convenient, retained, tube, rendered, adapted, favorable, maintained, controlled, direction, efficient, thorough, middle, follows, heavy, preferable, requiring