328 EARLE C. GREGG, JR. 



time, but also to be able to preset it to some other intensity. This is 

 generally done by calibrating the field at the point in question in 

 terms of the electrical current delivered to a magnetostrictive rod or 

 the voltage applied to a piezo crystal, whichever source is used. 

 Once, however, the geometrical conditions or the frequency is changed, 

 the calibration will change. 



C. BIOLOGICAL EFFECTS OF ULTRASONIC VIBRATIONS 



Since so many survey articles and resumes {2,3,18,19,24) of the 

 biological action of ultrasound have appeared in the literature, it will 

 suffice here merely to mention some of the outstanding experiments 

 and techniques and to attempt to explain some of the observations. 

 Unfortunately in some experiments, little if any data were reported 

 on the sound field used and as a result attempts to determine the 

 fundamental factor or factors responsible for some biological actions 

 have met with little success. First, it will be worth while to reiterate 

 the properties of a high energy sound field. Vibration of this sort is 

 characterized by extremely high pressures and large accelerations of 

 the particles of liquid in the field. These in turn produce cavitation 

 and, if dissolved gas is present, intense local agitation, high local 

 temperatures, and possibly electrical potentials. The net result is 

 an exhibition of lethal and sterilizing effects, strong dispersive power, 

 degassing processes, thermal and oxidizing effects, and coagulation. 



1. Lethal and Sterilizing Action 



The first biological effects of high intensity, high frequency sound 

 waves were observed by Wood and Loomis (11), who reported that 

 protozoa were paralyzed or killed depending on the length of ex- 

 posure. They advanced the concept that all protozoa did not re- 

 spond alike since the smaller ones could "ride" the waves and not be 

 greatly affected. They further felt that rupture of the larger bodies 

 was probably due to variations in direction and magnitude of the 

 forces (pressure) applied to different points of the body. Bacteria 

 apparently were not affected because the entire organism was sub- 

 jected to the same force. Other investigators have supported the ob- 

 servation that larger protozoa were affected while smaller ones were 

 not. 



In 1931, Harvey and Loomis (10) made high speed photomicro- 

 graphs of living cells subjected to ultrasound and found that the de- 



