That book must have been THE ADVENTURES OF TOM SAWYER.

I wrote the first half of it in '72, the rest of it in '74.

My machinist type-copied a book for me in '74, so I concluded it was that one.
That early machine was full of caprices, full of defects--devilish ones.
It had as many immoralities as the machine of today has virtues.

After a year or two I found that it was degrading my character, so I thought I would give it to Howells.

He was reluctant, for he was suspicious of novelties and unfriendly toward them, and he remains so to this day.