1. In two rabbits subjected to prolonged injections with crystalline egg albumin the antibodies in one showed progressive changes such as noted in an earlier paper; the antibodies in the other did not.
2. The significance of this behavior in the production of sera for therapeutic use is pointed out.
3. Quantitative studies are reported on the low grade or incomplete antibody present in the early stages of immunization of a horse with egg albumin.
4. Quantitative studies on the flocculating antibody from later bleedings from the horse are given, and the dissociation of the soluble pre-zone compounds by rabbit anti-egg albumin is studied. Rough velocity estimations are reported.
5. The bearing of the findings on the mechanism of precipitin and flocculation reactions and of the Danysz effect is discussed in terms of the union of multivalent antigen with multivalent antibody.