Kline (1921) used 'meaningful' material (states and capitals, counties and county seats, and books and authors) in a study of interference effects of associations. He found that if the first associative bond had a recall power of 10 percent or less it facilitated the second association, if it had a recall power of 15 percent to 40 percent the inhibitory power was small, if it had a recall power of 45 percent to 70 percent the inhibiting strength approached a maximum, if the recall power was 70 percent to 100 percent the inhibition was of medium strength and in some cases might disappear or even facilitate the learning of a new associaiton.