The Mechanism of the Lethal Effects of Ultrasonic Radiation

Abstract

That the lethal effects of ultrasonic waves on protozoa and other single cells could be traced to the cavitation of dissolved gas, has recently been discovered by Johnson. 1 Any gas suffices, apparently; there is no specificity of cavitated oxygen as was found for acceleration of chemical reactions by Schmitt, Johnson and Olson. 2 We have repeated the experiments of Johnson and are able to confirm his results fully. The present communication extends these observations and examines the mechanism of the lethal effect. A large number of microorganisms were tested, including various types of protozoa, rotifers, copepods, Daphnia, etc. In addition to these a number of eggs and embryos of frogs and snails were treated. About 10 cc. of the fluid containing the material to be tested was placed in a glass tube and radiated at atmospheric pressure, and at pressures of 60-80 lb. per square inch. After the minimum lethal dose for those radiated at atmospheric pressure was determined, it was found that an exposure many times this dosage had no effect upon cells radiated under 60-80 lb. pressure. Radiation of frog embryos yielded results which seem to indicate that radiation affects the head region rather preferentially, and that there is a definite selective interference in organogenesis. A study of these effects will be reported later.

To test the possibility that the function of the cavitated bubbles is to reflect the waves from their surfaces and thus tend to concentrate the radiation locally, two types of experiments were performed. In the first, cells were radiated in a suspension of infusorial earth, the suspended particles ranging from very small to relatively coarse. In the second, paramecia were allowed to ingest Chinese black which packed the food vacuoles with solid granules.