174 THE PHYSICS OF VIRUSES 



In Oster's work, the virus was exposed to high-intensity sound 

 at 9,000 cycles/sec. Under this treatment, the viscosity and 

 stream birefringence of the virus preparation were both observed 

 to diminish. As the sonic treatment was continued, the virus was 

 observed in the electron microsco])e. It was clear that the average 

 rod length had diminished and, in particular, that apparently 

 rods broke into half sections, quarters, and eighths. Oster ana- 

 lyzes this process into a successive series and shows that at any 

 particular fractional length there is an optimum time for which 

 this length will predominate. Some of his data are shown in Fig. 

 7.2. It can ])e seen that sonic action affords a method of ])roduc- 

 ing a change in rod length in a somewhat controlled way. From 

 observing the ability of various sonically treated preparations to 

 produce local lesions, Oster concludes that the infectious particle 

 is 2,800 A in length. 



It is of interest that bringing the treated virus to the isoelectric 

 point for three days at 37° C causes broken rods to aggregate. 

 Oster found that these aggregated particles are not infective. 

 They can be seen to be curved somewhat when observed on elec- 

 tron micrographs. These curved aggregates indicate, as Oster 

 points out, that the length of 2,800 A corresponds to that of the 

 infectious particle. 



Newton's studies were made with 7-mc sound produced by 

 exciting a quartz crystal. The virus was placed in a Lucite irra- 

 diation cell immersed in transformer oil, and probably some in- 

 ternal heating occurred, although the outside was water cooled. 



