Who said "I've got blisters on my fingers!" and why did they say it?

Who: Ringo Starr said it after the take of the song "Helter Skelter" that would appear on the album The Beatles, released in 1968, better known as "the White Album."

Why: Ringo drummed very hard on this song. It was the hardest song they had recorded to date (hard as in Heavy Metal).

https://www.youtube.com/watch?v=E0x978oZa3Y&feature=youtu.be
https://www.youtube.com/watch?v=SWY1iuPAkyM

Mark Lewisohn 'The Complete Beatles Recording Sessions' p.154:

Monday 9 September

'If 'Revolution 9' was John's excursion into mayhem on 'The Beatles', 'Helter Skelter' was Paul's. But it was Ringo who added the perfect finishing touch. Having drummed as if his life depended on it, his "I've got blisters on my fingers!" scream was preserved as the song's great climax.

Chris Thomas recalls, "While Paul was doing his vocal, George Harrison had set fire to an ashtray and was running around the studio with it above his head, doing an Arthur Brown! All in all, a pretty undisciplined session, you could say!"

http://www.beatlelinks.net/forums/archive/index.php/t-5385.html

Ringo is the correct answer, but the point that no one has made yet is that the original take of Helter Skelter was 26 MINUTES LONG! A Herculean task for any drummer, no matter how hardened the callouses on the hands were.

For the album version, recorded on September 9, eighteen takes of approximately five minutes each were recorded, and the last one is featured on the official LP. "After the eighteenth take, Ringo flung his sticks across the room and shouted, 'I've got blisters on my fingers!'