What does "chemotaxis" mean?

Chemotaxis: The sensitiveness exhibited by small free-swimming organisms, as bacteria, zoöspores of algæ, etc., to chemical substances held in solution. They may be attracted (positive chemotaxis) or repelled (negative chemotaxis). -- Chem`o*tac"tic (#), a. -- Chem`o*tac"tic*al*ly, adv.