Sentence:  Interestingly enough , the effect of the digitalis glycosides is inhibited by a high concentration of <WSD>potassium</WSD> in the incubation medium and is enhanced by the absence of potassium ( Wolff , 1960 ) . 
Meaning of the word marked with <WSD> tags:  a light soft silver-white metallic element of the alkali metal group; oxidizes rapidly in air and reacts violently with water; is abundant in nature in combined forms occurring in sea water and in carnallite and kainite and sylvite