Observations on Antityphoid Vaccination

1. Metchnikoff and Besredka's living sensitized vaccine produces a typhoid cholecystitis when injected directly into the gall bladder of rabbits. It is therefore infectious. 2. Rabbits cannot be successfully immunized with this vaccine against direct gall bladder infections. Accordingly, rabbits cannot be used to test immunity in this way. 3. The strain used in the Army vaccine is pathogenic, relatively avirulent, and distinctly toxic. Its efficacy is believed to depend on its toxicity. 4. Vaccinations in those who have had typhoid and revaccinations produce more severe local reactions than original vaccinations in some instances. 5. The typhoidin skin test is not believed to be an index of true immunity, but rather an indication of typhoid proteid sensitization, which is not so complete, so permanent, or so specific as true immunity.