FIG. 2.

Determination of the number of particles in aggregates following incubation of T. pallidum in sera from animals with various degrees of immunity to challenge reinfection, in NRS, and in IRS. The total number of particles from 20 to 24 concave outer membrane fracture faces was determined. Numbers of particles within an aggregate were determined by directly counting the particles and by determining the surface area of an aggregate in comparison to the surface area of an individual particle.