“…Experiments by Dr. I. Ardelean, using the bactericidal technique employed in this laboratory (49), have also shown that in vitro these sera possess marked opsonizing properties versus young, fully encapsulated organisms. Unpublished experiments carried out several years ago by one of us (J. F. E.) had indicated that, in mice, 16 hours after establishment of an infection the therapeutic effect of Antipneumococcus Type I rabbit sera was superior to that of Antipneumococcus Type I horse sera which by various tests (agglutination, precipitation, effect in the bactericidal system, and mouse protective power) were of the very large numbers of cocci which may be present in the cerebrospinal fluid.…”