a fume hood is provided having an air intake and an air exhaust communicating with each other through the interior of a fume hood cabinet by way of a by - pass passageway and open front on said cabinet . a plurality of sashes are carried by track means which enable them to move selectively horizontally relative to each other across the open front of the fume hood cabinet to variably open and close the same selectively and relative to the open front . means connected to the sashes provided for coincidental selective movement therewith to variably close and open the communication of air between the air intake and air exhaust through the by - pass passageway of the fume hood cabinet according to the selective movement of said sashes .