This is from 茨海{ばらうみ}小学校 by 宮沢賢治, probably written almost 100 years ago.
「どうぞスリッパをお召しなすって。只今{ただいま}校長に申しますから。」
My question is about お召しなすって. I think 召す is 尊敬語 meaning "to wear" in this case. I know there are some patterns like お~になる and お~する. Is なする a corruption of なさる?