Sentence:  Interestingly enough , the effect of the digitalis glycosides is inhibited by a high concentration of potassium in the incubation <WSD>medium</WSD> and is enhanced by the absence of potassium ( Wolff , 1960 ) . 
Meaning of the word marked with <WSD> tags:  (bacteriology) a nutrient substance (solid or liquid) that is used to cultivate micro-organisms