Rabbits were bred at The Rockefeller Institute with special relation to protection from exposure to Bacterium lepisepticum. These healthy rabbits were then submitted to intranasal instillation of a given dose of cultures of Bacterium lepisepticum. The results of the inoculation were various according to the natural degree of resistance of the individual animals.

The following graded effects could be distinguished: Some of the animals became (1) short time carriers of Bacterium lepisepticum; others (2) long time carriers of the same organism; some developed (3) local nasal infection (snuffles) of short duration; others (4) local nasal infection (snuffles) of long duration; while yet others had (5) snuffles, followed by pneumonia and signs of general infection after a few weeks; and finally there were instances of (6) local nasal discharge attended by general infection and pneumonia after a few days.

The effects produced in any given healthy stock depend also upon the degree of virulence of Bacterium lepisepticum of which great differences exist among the same and different strains.

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