ACOUSTIC SURGERY is the use of sound in place of the scalpel to perform such tasks as destroying tumors and stopping internal bleeding. At last week's joint meeting in Seattle of the International Congress on Acoustics and the Acoustical Society of America, Gail ter Haar of the Royal Marsden Hospital in England (011-44-181-642-6011) described a clinical trial in which focused sound waves destroyed parts of liver, kidney, and prostate tumors in 23 patients. Just as sunlight sent through a magnifying glass can burn a leaf placed at the spot where the light converges, sound broadcast through a specially shaped set of speakers can converge inside the body to create a region of intense heat that can destroy tumor cells. The spot is so small that there is only a boundary of six cells between destroyed tissue and completely unharmed tissue--a precision that is finer than any scalpel. Ter Haar said the next phase is to attempt complete destruction of tumors in the liver and prostate. (See www.acoustics.org/haar.htm) Meanwhile, Roy Martin of the University of Washington (206- 685-1883) discussed the use of ultrasound to stop internal bleeding in the liver. Just as a grill heats a steak, the sound waves heat the bleeding area to create chemical and physical changes that cauterize it. Otherwise, liver surgery is often hampered by bleeding, Martin said.