13 



Mechanical Resonances of 

 Biological Cells 



I. Experimental Basis 



In Chapter 12, it was shown that single biological cells in suspension are 

 ruptured if the ultrasonic field is strong enough to produce cavitation. 

 There seems little doubt that the destructive effects are produced by the 

 shearing forces in the immediate neighborhood of these cavities, even 

 though the exact details of how this occurs remain uncertain. Qualita- 

 tively, the same results are obtained at 1 kc/sec and 1 mc/sec. Most 

 studies of ultrasonic rupture of single cells have employed only one 

 frequency or, at best, an isolated set of frequencies. However, certain 

 studies by the author and others have shown that frequency effects do 

 occur; that is, at certain characteristic frequencies the cells of a particular 

 type are ruptured much more readily than at neighboring frequencies. 

 These optima are customarily referred to as resonances ; they depend on 

 the cell type and size. 



Most mechanical structures have resonances. These in turn form a 

 basis for studying the mechanical system. Mechanical resonances are 

 used to investigate crystal structure, properties of liquids, and internal 



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