FIG. 2.

Percentages of Ure⁺ and Ure⁻ Y. pestis cells recovered from the spleen of individual mice. OF1 mice were infected s.c. with an equal number of Ure⁻ (strain 6/69r) and Ure⁺ (strain 6/69 U5.1) Y. pestis cells. Two separate experiments were performed with a bacterial inoculum of 115 and 85 bacteria per animal, respectively. The percentage of Ure⁺ (black columns) and Ure⁻ (grey columns) bacteria in spleens of moribund animals was determined as described in Materials and Methods. Results obtained for each individual mouse are presented.