SONIC AND OSMOTIC EFFECTS ON VIRUSES 171 



irradiation ajjparatus is described fully by Krueger, Brown, and 

 Scribner (1941). 



True supersonic oscillations are j)roduced by the electrical 

 excitation of a quartz crystal, which changes thickness along 

 a certain axis when an electric field is applied along that direc- 

 tion. The thickness of the crystal determines the frequency of 

 oscillation, the thinner the crystal the higher the frequency, and, 

 in practice, the only limit to the power available at frequencies 

 below 1 mc lies in the power supi)ly for the oscillator, which 

 becomes cumbersome and expensive if power of the order of a 

 kilowatt is needed. 



The crystal and the associated electrodes are immersed in 

 transformer oil. Above the crystal is ])laced a cell with thin 

 upper and lower walls of any kind of plastic membrane, and the 

 virus is suspended in solution in the cell. Power is then turned 

 into the oscillator, and irradiation allowed to j)roceed inter- 

 mittently (to control the temi)eratiire rise) for as long as is 

 needed. The arrangements are briefly described by Newton 

 (1951). 



Sonic Effects on Viruses 



An early observation of the effect of high-frequency sound 

 on tobacco mosaic virus was re})orted by Takahashi and 

 Christensen (1934) who subjected TMV to 9,000-cycle sonic 

 action. They found that the recorded number of local lesions fell 

 from 1,200 to 584 in 30 min, to 52 in GO min, and to zero in 2 hr. 

 The experiment was confirmed by Stanley (1934) who showed, 

 however, that when the virus preparation was sealed in a vacuum 

 and then irradiated almost no inactivation at all was found. It 

 seems, therefore, that the inactivation is to be associated with 

 cavitation. 



To see how this can act, consider a small region of dissolved 

 gas near the surface of the long, rod-shaped virus. Under high 

 pressure, the gas is firmly ])art of a tight structure comprising the 

 liquid and virus, with quite strong liquid-virus forces operating. 

 As the pressure goes sharjily negative, a gas cavity rapidly forms 

 and forces the liquid apart. This can readily break the virus, 



