In the experiments described above, we found with respect to tissue culture rabies virus that 1 cc., which contains approximately 50,000 mouse intracerebral lethal doses, properly irradiated, was required to immunize a mouse; 500 cc., which contain 25,000,000 doses, were required to immunize a 20 pound beagle dog.
Tissue culture virus concentrated ten times proved capable of immunizing mice in a dose one-tenth as large as that required for unconcentrated culture virus.
Brain virus suspensions were centrifuged so as to remove a large part of the tissue particles without striking loss in the virulence of the supernatant. The centrifuged supernatants of 1 to 5 per cent brain virus suspensions were irradiated so as to destroy virulence and yet retain immunizing potency.
Irradiated supernatants of mouse brain virus proved capable of immunizing mice as well as or better than similar supernatants treated with chloroform.
0.1 cc. of a 1 per cent irradiated dog brain virus containing approximately 50,000 mouse intracerebral lethal doses immunized mice effectively.