Abstract
Accumulating evidence indicates that an enhanced resistance to bacterial infection may be produced locally as well as generally. To gain further information as to the mechanism of this local immunity we have immunized rabbits intrapulmonically, subcutaneously and intravenously with a pneumococcal vaccine (Type I) and at a later period have tested the resistance of these animals to living pneumococci introduced intratracheally. We have also attempted to determine the fate of the pneumococci, both as to their retention within the lungs and their rates of appearance and disappearance in the blood stream.
Adult male rabbits weighing from approximately 3000 to 4000 gm. were immunized daily for from 4 to 6 days by injections of one cc. of a formolized vaccine of pneumococci. The vaccine was prepared by growing the pneumococci in Kolle flasks and adding 0.2 cc. of formalin to each 100 cc. of the bacterial growth suspended in 0.85% solution of sodium chloride. The intratracheally treated animals were immunized by means of a curved metal tube introduced into the trachea through the mouth; the others were immunized by subcutaneous and intravenous injections of similar amounts of the vaccine. The turbidity of the vaccine was between that in tubes 1 and 2 of the McFarland nephelometer. From 5 to 15 days after the final treatment the animals were infected in groups of 4, consisting of one normal rabbit and an animal immunized by each of the 3 ways mentioned. The 24-hour growth from a blood agar slant of a living pneumococcus culture, Type 1, was suspended in 8 cc. of sterile broth, and 2 cc. was then introduced intratracheally into each of the 4 animals through the metal tube inserted into the trachea. Blood was obtained by cardiac puncture at 5, 10, 15, 30, 45, and 60 minute intervals after infection and cultures made by plating duplicate amounts of one cc. with veal infusion agar, pH 7.6.
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