1.
Epidemiological data suggest that yaws protects against syphilis.
2.
The recent demonstration of a true immunity in syphilis throws new light on this question.
3.
Experimentally, a partial immunity against syphilis can be demonstrated in rabbits which have been infected a long time with yaws and cured by arsphenamine.
4.
The subject of strains must be taken in account, both in yaws and syphilis.