12:4/ Destructive Effects of High Intensity Ultrasound 229 



TABLE I 

 Ultrasonic Fragilities of Various Cells 



* Destruction interpreted to mean removal of tail from sperm cell. 



The lowest NaCl concentration at which lysis does not occur is an osmotic 

 measure of fragility. Both osmotic and ultrasonic methods show that 

 the fragility of human red blood cells increases as the cells age. The 

 ultrasonic measurements show this increase sooner than do the osmotic 

 ones. Thus, the two do not measure exactly the same properties of the 

 cell. 



The role of the cell surface in determining fragility can be illustrated 

 dramatically by the protozoan, Blepharisma. These are pink ciliates 

 somewhat similar to paramecia in shape. When a culture of blepharisma 

 is exposed to suitable narcotics (for example, morphine sulfate) the 

 animals shed their pink pellicles while retaining their shape, cilia, and 

 so on. They look even more like paramecia without their pellicles than 

 with them. The relative fragility of the animals is doubled after they 

 shed their pellicles. This indicates that although the pellicle does not 

 control the shape of the animals, it does contribute to their ability to 

 withstand mechanical disturbances. 



Although at most frequencies the relative breakdown rates are the 

 same, at certain frequencies, experiments with paramecia, blepharisma, 

 and red blood cells indicate greatly increased sensitivity to ultrasonically 

 induced cavitation. It seems natural to interpret these frequencies as 

 cellular resonances induced by cavitation. From a knowledge of these 

 resonances, it should be possible to determine the elastic properties of 

 the cell walls. This subject is sufficiently specialized for the entire 

 next chapter to be devoted to it. 



Thus, the rupture of single biological cells in a cavitating ultrasonic 

 field has been useful not only for the preparation of enzyme and particu- 

 late extracts, but also to study the fragility and elastic properties of the 

 outer surfaces of living cells. 



