PROTECTION AGAINST HUNTING 3II 



notations). However, mice which had such positive sera, and had 

 negative sera after 3 months without further immunization, 

 again had strongly positive sera such as 512 (+ + + 8-32) or 

 512 (+ + + 16-128) after reinjection with A lyophilized new- 

 borns. This fact is of importance, for it demonstrates that lyo- 

 philized newborns contain antigens able to induce formation of 

 anti-strain antibodies and, as a consequence, that sera AN-BI, 

 AN-BII and AN-BIII must have contained strain-specific 

 (anti-H-2'' antigens, particularly D) antibodies, even when they 

 were not able to give direct haemagglutination. On the other 

 hand, this might also explain why sera AN-BI and AN-BII were 

 much weaker than serum ANB+ T. 



B. Imniuno toxicity 



The direct action on A newborns of minute amounts (mm.^ 

 doses) of CBA anti-A sera was ascertained by intravenous injection 

 of these sera alone (without cells) in A newborns, at doses higher 

 than the ones used for enhancement. Serum AN-BIII was 

 particularly studied in this respect. The results of a typical 

 experiment are given in Table III. 



From this table, it is clear that serum anti-newborn-A is highly 

 immunotoxic for newborn A. In this particular case the dose 

 closest to the LD50 is i- 00 mm.^. The amount of serum required 

 for LD50 seems to be in a very narrow range since a dose of o- 80 

 mm.^ causes no death and dose of i • 20 mm.^ causes death of aU 

 injected animals. 



Doses less than i-oo mm.^, although they are not lethal, still 

 have a defmite depressive action on the weight curve — a depres- 

 sive action which seems to be completely overcome by day 15. 

 This immunotoxicity is specific for A-newborn strain-specific 

 antigens. The only control used, so far, has been CBA newborns 

 injected with doses of 2 to 10 mm.^ of CBA anti-A serum. No 

 mortality occurred from these injections and no decrease in the 

 weight curve. Serum AN-BI, whose protective effect was slight, 



