Metchnikoff and Roux, followed by Lassar and Neisser, have demonstrated conclusively, by numerous and diversified experiments, that syphilis may be transmitted by inoculation to chimpanzees and other apes. It has been found that in the chimpanzee the period of inoculation varies between twenty-two and thirty-seven days; and, furthermore, that the disease may be transmitted from chimpanzee to chimpanzee. This means that it now has become possible to subject the "virus" or "contagium" of syphilis to more penetrating investigations with the view to obtain some idea of its nature, and thus pave the way for its actual demonstration.
So far, minute study of the material known to contain the infectious agent of syphilis has not yielded any information—organisms have not been found in the scrapings and juices of chancres and other lesions in either man or anthropoid. The thought naturally suggested itself that the syphilitic virus might be filterable, like the