1. The allergic irritability of the guinea pig (capacity of the animal to react to antigenic substances) is increased by infection with Bacillus abortus and a streptococcus, by the dead tubercle bacillus, and by intensive treatment with trypan blue, respectively. The effect of these influences, while definite, is less pronounced than that previously found for infection with the tubercle bacillus. The production of anti-sheep hemolytic amboceptor was used as the test reaction in these cases.
2. The allergic irritability of the guinea pig with reference to anti-typhoid agglutinin is increased by infection with the tubercle bacillus.
3. The allergic irritability of the rabbit with reference to anti-sheep hemolytic amboceptor is increased by an infection of suitable severity with the tubercle bacillus.
4. In the guinea pig the curve of antibody production is complex. Its peculiarities are developed during the production of antityphoid agglutinins as well as that of anti-sheep hemolytic amboceptor. In the latter case injections of antigen subsequent to the first give rise to a curve of production unchanged in form but somewhat affected in the time relations.
5. The effects of infection with Bacillus tuberculosis on allergic irritability with reference to anti-sheep hemolytic amboceptor are operative throughout a course of immunizing treatments. The successive increases due to the cumulative effect of repeated doses of the antigen are developed on a higher level. The end-result is that the animal with increased irritability furnishes more antibody not only in response to the initial injection of antigen as previously described, but an absolute increase over the amount attainable by a comparable number of treatments in series. That portion of the final result contributed by the increase in allergic irritability appears to be no less, and may even in instances be somewhat more than that due to the earlier doses of the specific antigen.