But it's growing cool.

Haven't you something hotter ?" Just five seconds later Reade regretted his rashness, for, snatching off the first poultice, the squaw slapped on a second that seemed, in some way, ten times more powerful---and twenty times hotter.
"It's queer what an awful amount of heat a squaw can get out of a kettle of hot water, thought the suffering boy.

I'll wager some of the heat is due to the herbs themselves.

O-o-o-o-ow! Ouch!" For now the third poultice, most powerful of all, was in place, and Mrs.Squaw was binding it on as though she intended it never to come off.
Two minutes after that Tom Reade commenced to retch violently.
With a memory of the messes that he had swallowed he didn't wonder.
The squaw now stepped outside, calling for coffee.

This was brought.