‘Venerable Nāgasena, that one quality of the leech which you say he ought to take, which is it?’

‘Just, O king, as the leech, wheresoever it is put on, there does it adhere firmly, drinking the blood; just so, O king, should the strenuous Bhikshu, earnest in effort, on whatsoever subject for meditation he may fix his mind, call that subject firmly up before him in respect of its colour, and shape, and position, and extension, and boundaries, and nature, and characteristic marks, drinking the delicious draught of the ambrosia of emancipation. This, O king, is the quality of the leech he ought to have. For it was said, O king, by Anuruddha, the Elder:

“With heart made pure, in meditation firm,
Drink deep of freedom’s never-failing draught.”’