THE SURFACE OF VIRUSES 139 



few, it should be possible by deuteron bombardment, and 

 nearly as well by electron bombardment, to produce an inactive 

 virus which will stimulate antibody formation very nearly as 

 efficiently as the active virus itself. This has been tried, quite 

 independently of the above work, by Traub, Friedemann, 

 Brasch, and Huber (1951). These workers have prepared a 

 rabies vaccine by electron bombardment. The technique used is 

 to harvest brains from mice injected intracerebrally with stock 

 virus, waiting until 24 hr after the first symptoms developed. 

 These were ground up, broth added, frozen in polyethylene bags, 

 and exposed to 3-Mev electrons in the frozen condition on a 

 solid COo support. They were then thawed and tested for 

 antigenicity. This was done by injecting at various dilutions into 

 rats and then injecting challenge doses of the original virus 

 preparation at various concentrations. The results are shown in 

 the table. 



It can be seen that approximately 10,000 times as many 

 original infectious virus particles are needed after such vaccina- 

 tion. 



The amount of electron dose was found to diminish the loga- 

 rithm of protection. If this fits a semilogarithmic relation (and 

 the data are not complete enough to permit this deduction), then 

 26 X 10*^ rep are needed to cause a drop in the serological 

 potency to 37%. This is 1.59 X 10^^ primary ionizations/cm^ 

 so that the inactivation volume *is 1/1.59 X 10^^ or roughly 

 6 X 10~^° cm^, corresponding to an equivalent molecular weight 



