Morphology of Treponema pallidum.

In recent years many investigations have been carried out on the morphology of Treponema pallidum by means of the electron microscope, and the use of ultra-thin sections has shown up a number of structural details. However, there is still need for much more evidence before the internal structure of treponemes can be elucidated fully and the functions of the structures interpreted. To provide such evidence, the authors have examined under the electron microscope negative-stained treponemes and ultra-thin sections, using both cultivated strains and treponemes obtained direct from syphilids in people suffering from fresh secondary syphilis. It has been shown that treponemes have a complex structure. T. pallidum has a two-layered outer wall, a cytoplasmic membrane proper, cytoplasm and a bunch of fibrils following a different path in different places on the treponeme. The sites of insertion of the fibrils (the basal granules) were investigated; structures similar to mesosomes and nucleoids were found. Cysts and granular forms are described.