Complex sentence: He founded the Institute after hearing about a boy who had regained the use of his legs, through a treatment known as hydrotherapy, which involves the use of water for soothing pains and treating diseases.
Split into simpler sentences: He founded the Institute after hearing about a boy who had regained the use of his legs, through a treatment known as hydrotherapy. Hydrotherapy involves the use of water for soothing pains and treating diseases.