New source for positive controls used for the identification of spirochaetes in tissue sections

Lyophilized T. pallidum is recontituted or purchased as a suspension, evenly dispersed, made into smears using alcohol-cleaned slides and a bacteriological platinum wire loop. Smears are air dried for 15 minutes and fixed in concentrated formaldehyde fumes for 30 minutes and stored at room temperature. These preparations are used as positive controls for conventional silver impregnation techniques recommended for spirochaete detection in tissue sections.