The "cold times" in Jim's life might be that he got lost in the wild.

"The wind has bitten into his skin" means that it was so cold and it was like if the wind was biting into his skin.

I think that the writer has compered a well to Jim's knowledge because a well is very deep so he must be very wise.

When Jim drinks from the well he's actually scraping his teeth together to make a fire.

His breathing is pleading means that he's pleading for something.

I think to survive he needs to live like the caveman.