Summary

• 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.