In this system I use three distinct types of cards, each 3 in. X5 in. and of 'medium weight,' which, for convenience of referencehere, I shall designate 'condition card' (Fig. 1, card 1), 'barredcard' (Fig. 2, card 1), and 'extension card' (Fig. 1, card 2; Fig.2, card 2). The cards for these plates were not selected withreference to contemporaneity, which I hope will not confuse, butselected with a view to illustrating to better advantage the plan ofamplifying notes on the 'extension cards.'