“…The inhibition has been often attributed to various extracellular products including polysaccharides (Biswas, 1957Bishop, Adams & Hughes, 1957Tischer, 1965 ;Moore & Tischer, 1965) and nitrogenous compounds (Watanabe, 1951 ;Fogg, 1952Fogg, . 1962Goryunova & Rzhanova, 1964;Fay, Kumar & Fogg, 1964;Gorham, 1964 ;Walsby, 1965 ; Dr. W. Junk b.v .…”