Our understanding of syphilis has undergone marked change of late years. Yet we still have more to learn than we already know and there is urgent need for new lines of investigation. The etiology of certain lesions that a few years ago were in dispute has been cleared up by the Wassermann test. Recent experimental animal researches and thousands of spinal fluid examinations have definitely established the fact that the invasion of the nervous system occurs in the early stages of the disease. Syphilologists are now quite generally agreed that we must consider different strains of the Spirochaeta pallida that have special predilection for special system, organs or tissues, just as we accept a bovine and human type of tubercle bacilli and numerous types of cocci and bacilli with special affinity for certain tissues. These facts explain many different phenomena observed in cerebrospinal and visceral syphilis.
The study of the