While we successfully isolated a certain filtrable agent by inoculation to guinea pigs of emulsion of choriocarcinoma, in order to elucidate as to whether or not this agent is choriotropic, we performed the neutralization or cross-neutralization test with serum of choriocarcinoma patients or with filtrable agent from stomach cancer. For the neutralizaion test of filtrable agent isolated from guinea pigs, to which the successive inoculation of emulsion of tumor tissue of choriocarcinoma had been performed, with serum of choriocarcinoma patients, the emulsion of the lungs and brains of the guinea pigs of the seventh generation after having passed through Seitz E. K. filter were employed. In regard to cross-neutralization with filtrable agent isolated from guinea pigs which were successively inoculated, those of sixteenth generation after having passed through the filter were employed. A anti-choriocarcinoma-agent serum of rabbits we first obtained 2 cc of supernate of emulsion made from lungs and brains of guinea pigs of the twelvth to nineteenth generation each after having passed through Seitz E. K. filter, and then we obtained the serum from 2 rabbits 14 days after the last injection which had follwed 8 times injections previously performed into the auricular veins of rabbits with 10 days intervals.
The filtrable agent of stomach cancer was obtained after having passed the brains of guinea pigs as usual procedure. The anti-stomach cancer filtrable agent serum of rabbits were obtained from serum of rabbit which were repeatedly injected intravenously by the emulsion of rabbits of seventeenth generation as with the case of choriocarcinoma. The following results summarily were obtained. In the neutralization test of choriocarcinoma filtrable agent with serum of choriocarcinoma patients the agent was almost perfectly neutralized, showing the value of ID(50)>10(-2.0). The neutralization with serum of the normal women contrarily showed ID(50)=10(-3.75). The former revealed the remarkably high value of neutralization body. The crossneutralization test with the filtrable agent isolated from human stomach cancer as the control experiment disclosed that the neutralization test of choriocarcinoma filtrable agent with serum of normal rabbits showed ID(50)=10(-5.0), and that those with anti-stomach cancer filtrable agent serum of rabbit showed ID(50)=10(-4.0), and also that the neutralization test of choriocarcinoma filtrable agent by anti-choriocarcinoma filtrable agent serum of rabbit revealed ID(50)=10(-2.0). From the result shown above it is highly understandable that the value of the neutralization test of choriocarcinoma filtrable agent by anti-serum of rabbit for choriocarcinoma agent is more striking compared with those by 2 other kind of anti-serum. The neutralization test of stomach cancer filtrable agent by anti-stomach cancer serum of rabbit, furthermore, disclosed ID(50)=10(-3.45) and that by anti-choriocarcinoma agent serum of rabbit showed ID(50)=10(-4.25) and also that by serum of normal rabbit was ID(50)=10(4.0) in value. Therefore, the establishment of the neutralization test apparently failed between the choriocarcinoma filtrable agent and stomach cancer agent. From the result shown above, we would like to conclude that the filtrable agent isolated from choriocarcinoma after passage through the brain of guinea pigs has the potentiality to neutralize and moreover is choriotropic in nature.