The years 1903, 1905 and 1907 each marks a definite step in the advancement of our knowledge of syphilis.
With Metchnikoff's and Roux's inoculation experiments on the higher apes in 1903 the scientific world again renewed its efforts to discover, if possible, the cause of syphilis, and when Schaudinn and Hoffmann announced the Spirochœta pallida, in 1905, the diagnosis of primary syphilitic lesions was placed on a definite basis.
The establishing of the Spirochœta pallida as the etiologic factor in syphilis has been fraught with much criticism, because the discovery did not conform to Koch's postulates. The work of Metchnikoff, Roux, Neisser and many others stands out in bold relief and has put the specificity of the Spirochœta pallida on so firm a basis that, notwithstanding their inability to culture the organism, it is now accepted by syphilographers the world over.
The complement-fixation test as discovered by Bordet and Gengou,
CORBUS BC. TWO YEARS' EXPERIENCE WITH THE WASSERMANN REACTION IN PRACTICEA PRELIMINARY REPORT ON FIFTY-SEVEN CASES TREATED FROM THE STANDPOINT OF THE WASSERMANN REACTION. JAMA. 1910;55(10):849–853. doi:10.1001/jama.1910.04330100035010