The Leeches Cling On

(from ebookjapan):
Mitsue and her sister Hiromi come to the countryside for summer vacation and become concerned about their grandmother's mysterious cure for their mother, who is suffering from a serious illness that doctors have given up on. When Mitsue and Hiromi learn that their grandmother used to treat their mother by having a leech that sucks bad blood crawl on her body, they feel sorry for her and dump the leech in a pond while their grandmother is away. ......?