The fact of the heredity of syphilis was known to Paracelsus, who, in the year 1560, asserted that this disease was due to some unknown virus circulating in the blood, which also infests the semen and during conception is transmitted with it to the fetus.
Still, at the present time, we are not able to recognize positive laws as to the methods and conditions of the transmission of hereditary syphilis, and must fall back on theories based entirely on empirical conclusions. Until the specific micro-organism of syphilis is demonstrated scientifically and beyond doubt, these theories will never be more than probabilities—the more so as we find ourselves heavily handicapped in the attempt to make use of our clinical material. The protean nature of syphilis, where we might say that exceptions form the rule, the necessity to observe cases over periods of many years and finally our dependence
SCHALEK A. THEORIES OF THE TRANSMISSION OF HEREDITARY SYPHILIS.. JAMA. 1903;XL(20):1349–1351. doi:10.1001/jama.1903.92490200011002c