Adam Clarke on Isaiah 38:21

Let them take a lump of figs, etc. - God, in effecting this miraculous cure, was pleased to order the use of means not improper for that end. "Folia, et, quae non maturuere, fici, strumis illinuntur omnibusque quae emollienda sunt discutiendave." - Plin. Nat. Hist. 23:7. "Ad discutienda ea, quae in corporis parte aliqua coierunt, maxime possunt-ficus arida," etc. - Celsus, 5:11.

See the note on 2Kgs 20:7 (note). Philemon Holland translates the passage as a medical man: "The milke or white juice that the figge tree yieldeth is of the same nature that vinegre: and therefore it will cruddle milke as well as rennet, or rendles. The right season of gathering this milkie substance is before that the figs be ripe upon the tree; and then it must be dried in the shadow: thus prepared, it is good to break impostumes, and keepe ulcer open."