 induc tumour resist rat human sarcoma hs grown weanl rat treat cortison growth modifi prior inject tissu antigen activ immun produc human placenta embryon tissu antigen suspens rapidli grow human tumour respons human tissu vari foetal muscl spleen activ adult plasma inact patient extens malign diseas passiv protect produc human sera time challeng hs sera women abort characterist pregnanc continu term antisubst puerperium fifti case group rat rat embryon tissu antigen tumour challeng walker tumour variabl benzpyren-induc tumour pure wag rat isol case experi mice challeng irondextran induc mous sarcoma prior inject embryon mous liver placenta increas resist growth tumour tumour produc pure-line mous hand mous experi challeng crocker tumour prove neg suggest immun reaction plai caus abort 