Antisera against the Ehrlich Ascites Tumor*

Newborn rabbits were made immunologically tolerant to normal C3H mouse tissue and were subsequently immunized with the Ehrlich ascites tumor. Nonpretreated rab bits were also immunized with tumor. In addition, both tolerant and nonpretreated rabbits were given similar injections of normal tissue antigens. It wasfoundthat, in smallamounts,both tolerantand nontolerantanti-Ehrlich ascites tumor sera gave some protection to mice previously given inoculations of tumor. Neither of the antinormal tissue sera nor the normal rabbit serum gave this protection. However, when given in large amounts, the nontolerant antisera (either to Ehrlich ascites tumor or normal tissue) were immediately lethal to the vast majority of mice so treated, and normal rabbit serum or tolerant antinormal tissue serum had little effect of any kind, toxic or protective. On the other hand, the tolerant anti Ehrlich ascites tumor serum had only slight murine toxicity and was able to exert a greater protective effect on mice given inoculations of Ehrlich ascites tumor, by reason of its being able to be safely administered in large amounts.