INFLUENCE OF AGE FACTORS ON IMMUNIZABILITY OF MICE TO RABIES VIRUS.

1. W-Swiss mice 60 or more days old are more readily immunizable against rabies virus infection than 20 day old or younger mice; this difference in immunizability with increasing age is most conspicuous when vaccination with virulent virus is followed by intracerebral test infection and least apparent when vaccination with avirulent virus is followed by intramuscular test infection. 2. The titre of circulating neutralizing antibodies does not parallel the titre of immunity.