Holder, on the basis of his own experiences among Indian tribes,
as well as of wide inquiries among agency physicians, prepared a
table showing that among some thirty tribes and groups of tribes,
eighteen were almost or entirely free from venereal disease,
while among thirteen it was very prevalent. Almost without
exception, the tribes where syphilis is rare or unknown refuse
sexual intercourse with strangers, while those among whom such
disease is prevalent are morally lax. It is the whites who are
the source of infection among these tribes (A.B. Holder, "Gynecic
Notes Among the American Indians," _American Journal of
Obstetrics_, 1892, No. 1).

Syphilis is only one, certainly the most important, of a group of three
entirely distinct "venereal diseases" which have only been distinguished
in recent times, and so far as their precise nature and causation are
concerned, are indeed only to-day beginning to be understood, although two
of them were certainly known in antiquity. It is but seventy years ago
since Ricord, the great French syphilologist, following Bassereau, first
taught the complete independence of syphilis both from gonorrhoea
and soft chancre, at the same time expounding clearly the three stages,
primary, secondary and tertiary, through which syphilitic manifestations
tend to pass, while the full extent of tertiary syphilitic symptoms is
scarcely yet grasped, and it is only to-day beginning to be generally
realized that two of the most prevalent and serious diseases of the brain
and nervous system--general paralysis and tabes dorsalis or locomotor
ataxia--have their predominant though not sole and exclusive cause in the
invasion of the syphilitic poison many years before. In 1879 a new stage
of more precise knowledge of the venereal diseases began with Neisser's
discovery of the gonococcus which is the specific cause of gonorrhoea.
This was followed a few years later by the discovery by Ducrey and Unna of
the bacillus of soft chancre, the least important of the venereal diseases
because exclusively local in its effects. Finally, in 1905--after
Metchnikoff had prepared the way by succeeding in carrying syphilis from
man to monkey, and Lassar, by inoculation, from monkey to monkey--Fritz
Schaudinn made his great discovery of the protozoal _Spirochoeta
pallida_ (since sometimes called _Treponema pallidum_), which is now
generally regarded as the cause of syphilis, and