T ultrasonic radiation on normal and neoplastic tissues has been repeatedly demonstrated. (Since the scope and purpose of this paper does not call for an extensive review of the literature, specific references will be limited to those that bear directly on the present problem; recent review articles in English are avail-ab1e.l. 37 9) This study was designed to determine in living mice the relative susceptibility of various tissues to the destructive effects of ultrasonic waves and, specifically, to determine whether neoplastic tissues are more sensitive than normal tissues. T h e mouse was chosen for this study in order that ultrasonic energy could be administered simultaneously to almost the entire body.
Methods
The ultrasonic waves were generated by plane barium titanate slabs having a 1x1-in. surface area and so constructed as to resonate at frequencies of 0.5, 1.0, 1.5, 2.0, and 3.8 megacycles per second. T h e elements were piezoelectric and were electrically excited from a generator that was capable of continuous tuning from 0.5 to 5.0 megacycles per second.
The elements were housed in brass cylinders through which water could be circulated for cooling, but in the present studies the apparatus