Mallory's phloxine-methylene blue stain was used to differentiate colonies of Cowdria ruminantium in
midgut epithelial cells of nymphal Amblyomma hebraeum that had been infected as larvae. Gut tissues were
collected from nymphs that had fed on a susceptible sheep and were fixed in formol-saline on the day of
repletion. Paraffin sections, 3-4 μm thick, were then stained and this rendered colonies and cell nuclei densely
blue against a uniformly pink background of tick tissues. Colonies were easily distinguished from nuclei by their
specific morphology. This method of parasite visualization may be adapted to field-collected ticks for rapid
detection of C. ruminantium or to assays of susceptibility of tick populations to various strains of the organism.